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Abstract Microbial α-l-fucosidases catalyse the hydrolysis of terminal α-l-fucosidic linkages and can perform transglycosylation reactions. Based on sequence identity, α-l-fucosidases are classified in glycoside hydrolases (GHs) families of the carbohydrate-active enzyme database. Here we explored the sequence-function space of GH29 fucosidases. Based on sequence similarity network (SSN) analyses, 15 GH29 α-l-fucosidases were selected for functional characterisation. HPAEC-PAD and LC-FD-MS/MS analyses revealed substrate and linkage specificities for α1,2, α1,3, α1,4 and α1,6 linked fucosylated oligosaccharides and glycoconjugates, consistent with their SSN clustering. The structural basis for the substrate specificity of GH29 fucosidase from Bifidobacterium asteroides towards α1,6 linkages and FA2G2 N-glycan was determined by X-ray crystallography and STD NMR. The capacity of GH29 fucosidases to carry out transfucosylation reactions with GlcNAc and 3FN as acceptors was evaluated by TLC combined with ESI–MS and NMR. These experimental data supported the use of SSN to further explore the GH29 sequence-function space through machine-learning models. Our lightweight protein language models could accurately allocate test sequences in their respective SSN clusters and assign 34,258 non-redundant GH29 sequences into SSN clusters. It is expected that the combination of these computational approaches will be used in the future for the identification of novel GHs with desired specificities.

Abstract Despite recent advances in cryo-electron microscopy and artificial intelligence-based model predictions, a significant fraction of structure determinations by macromolecular crystallography still requires experimental phasing, usually by means of single-wavelength anomalous diffraction (SAD) techniques. Most synchrotron beamlines provide highly brilliant beams of X-rays of between 0.7 and 2 Å wavelength. Use of longer wavelengths to access the absorption edges of biologically important lighter atoms such as calcium, potassium, chlorine, sulfur and phosphorus for native-SAD phasing is attractive but technically highly challenging. The long-wavelength beamline I23 at Diamond Light Source overcomes these limitations and extends the accessible wavelength range to λ = 5.9 Å. Here we report 22 macromolecular structures solved in this extended wavelength range, using anomalous scattering from a range of elements which demonstrate the routine feasibility of lighter atom phasing. We suggest that, in light of its advantages, long-wavelength crystallography is a compelling option for experimental phasing.

The anisotropy of energetic particles provides essential information to help resolve the underlying fundamental physics of their spatial distributions, injection, acceleration, and transport processes. In this work, we report an energetic ion enhancement that is characterized by very large and long-lasting anisotropies observed by STEREO A and Solar Orbiter, which are nearly aligned along the same nominal Parker spiral. This ion enhancement appears at the rising phase of a widespread solar energetic particle event that was associated with the farside coronal mass ejection on 2022 February 15. According to our analysis, the long-lasting anisotropy resulted from the continuous injection of energetic ions from a well-connected particle source located beyond the STEREO A’s orbit. Solar Orbiter also observed an interval of very large anisotropy dominated exclusively by sunward streaming ions but with the additional implication that it detected the very early phase of ion injections onto magnetic field lines that newly connected to the particle source, which is likely the first reported event of this kind. These results further illustrate how energetic particle anisotropy information, in particular from multiple observer locations, can be used to disentangle the sources and transport processes of energetic ions, even when their heliospheric context is not simple.

Three-dimensional electron diffraction (3DED) from nanocrystals of biological macromolecules requires the use of very small crystals. These are typically less than 300 nm-thick in the direction of the electron beam due to the strong interaction between electrons and matter. In recent years, focused-ion-beam (FIB) milling has been used in the preparation of thin samples for 3DED. These instruments typically use a gallium liquid metal ion source. Inductively coupled plasma (ICP) sources in principle offer faster milling rates. Little work has been done to quantify the damage these sources cause to delicate biological samples at cryogenic temperatures. Here, an analysis of the effect that milling with plasma FIB (pFIB) instrumentation has on lysozyme crystals is presented. This work evaluates both argon and xenon plasmas and compares them with crystals milled with a gallium source. A milling protocol was employed that utilizes an overtilt to produce wedge-shaped lamellae with a shallow thickness gradient which yielded very thin crystalline samples. 3DED data were then acquired and standard data-processing statistics were employed to assess the quality of the diffraction data. An upper bound to the depth of the pFIB-milling damage layer of between 42.5 and 50 nm is reported, corresponding to half the thickness of the thinnest lamellae that resulted in usable diffraction data. A lower bound of between 32.5 and 40 nm is also reported, based on a literature survey of the minimum amount of diffracting material required for 3DED.

The Main protease of SARS-CoV-2 is key for viral replication, but its maturation process is still not completely understood. Here, the authors not only reveal unique details from the first step of maturation, but also demonstrate how different classes of inhibitor can block this step.

BepiColombo mission had two Venus flybys on its way to Mercury. Here, the authors show that during its second flyby of Venus BepiColombo has crossed the stagnation region, which was predicted by the models.

Purpose: The aim of this study was to establish guidelines for the selection of cast and wrought-wire clasps for removable partial dentures (RPDs) that would be appropriate for clinically encountered undercuts and facial curvatures. Methods: Randomly selected discarded casts were collected and 30 premolars and 30 molars were surveyed, sectioned to a line representing the clasp and scanned using a flatbed scanner. The average clasp curvature and length for each group was determined and a three-dimensional model printed, to which wrought wire clasps of 0.9- and 1.0-mm diameter were adapted. Standard wax clasp patterns were adapted and cast in a stellite alloy. Each clasp was deformed beyond its proportional limit; and the forces exerted at that limit and at deflections of 0.25 mm, 0.5 mm, and 0.75 mm were measured, and a safety limit was calculated that would ensure elastic deformation at the required undercuts. Results: A table was produced with guidelines for those clasps that would provide the highest retentive force within the proposed safety limit. The highest forces were provided by cast clasps in a 0.25-mm undercut. Wrought round wire of 1-mm diameter provided the next highest retentive forces, in a 0.25-mm undercut for premolar clasps arms and 0.5-mm for molar clasps. Conclusions: The results provide valid guidelines for the use of combinations of clasp material and undercut that would exert the maximum retentive force without deformation for both short (premolar) as well as long (molar) clasps, for wrought and cast clasps.

Abstract Effective agents to treat coronavirus infection are urgently required, not only to treat COVID-19, but to prepare for future outbreaks. Repurposed anti-virals such as remdesivir and human anti-inflammatories such as barcitinib have received emergency approval but their overall benefits remain unclear. Vaccines are the most promising prospect for COVID-19, but will need to be redeveloped for any future coronavirus outbreak. Protecting against future outbreaks requires the identification of targets that are conserved between coronavirus strains and amenable to drug discovery. Two such targets are the main protease (Mpro) and the papain-like protease (PLpro) which are essential for the coronavirus replication cycle. We describe the discovery of two non-antiviral therapeutic agents, the caspase-1 inhibitor SDZ 224015 and Tarloxotinib that target Mpro and PLpro, respectively. These were identified through extensive experimental screens of the drug repurposing ReFRAME library of 12,000 therapeutic agents. The caspase-1 inhibitor SDZ 224015, was found to be a potent irreversible inhibitor of Mpro (IC50 30 nM) while Tarloxotinib, a clinical stage epidermal growth factor receptor inhibitor, is a sub micromolar inhibitor of PLpro (IC50 300 nM, Ki 200 nM) and is the first reported PLpro inhibitor with drug-like properties. SDZ 224015 and Tarloxotinib have both undergone safety evaluation in humans and hence are candidates for COVID-19 clinical evaluation.

The SARS-CoV-2 main protease is an important target for the development of COVID-19 therapeutics. Here, the authors combine X-ray crystallography and mass spectrometry and performed a large scale fragment screening campaign, which yielded 96 liganded structures of this essential viral protein that are of interest for further drug development efforts.

The human gut symbiont Ruminococcus gnavus displays strain-specific repertoires of glycoside hydrolases (GHs) contributing to its spatial location in the gut. Sequence similarity network analysis identified strain-specific differences in blood-group endo-β-1,4-galactosidase belonging to the GH98 family. We determined the substrate and linkage specificities of GH98 from R. gnavus ATCC 29149, RgGH98, against a range of defined oligosaccharides and glycoconjugates including mucin. We showed by HPAEC-PAD and LC-FD-MS/MS that RgGH98 is specific for blood group A tetrasaccharide type II (BgA II). Isothermal titration calorimetry (ITC) and saturation transfer difference (STD) NMR confirmed RgGH98 affinity for blood group A over blood group B and H antigens. The molecular basis of RgGH98 strict specificity was further investigated using a combination of glycan microarrays, site-directed mutagenesis, and X-ray crystallography. The crystal structures of RgGH98 in complex with BgA trisaccharide (BgAtri) and of RgGH98 E411A with BgA II revealed a dedicated hydrogen network of residues, which were shown by site-directed mutagenesis to be critical to the recognition of the BgA epitope. We demonstrated experimentally that RgGH98 is part of an operon of 10 genes that is overexpresssed in vitro when R. gnavus ATCC 29149 is grown on mucin as sole carbon source as shown by RNAseq analysis and RT-qPCR confirmed RgGH98 expression on BgA II growth. Using MALDI-ToF MS, we showed that RgGH98 releases BgAtri from mucin and that pretreatment of mucin with RgGH98 confered R. gnavus E1 the ability to grow, by enabling the E1 strain to metabolise BgAtri and access the underlying mucin glycan chain. These data further support that the GH repertoire of R. gnavus strains enable them to colonise different nutritional niches in the human gut and has potential applications in diagnostic and therapeutics against infection.

From 2022 March 18 to 21, NOAA Active Region (AR) 12967 was tracked simultaneously by Solar Orbiter at 0.35 au and Hinode/EIS at Earth. During this period, strong blueshifted plasma upflows were observed along a thin, dark corridor of open magnetic field originating at the AR’s leading polarity and continuing toward the southern extension of the northern polar coronal hole. A potential field source surface model shows large lateral expansion of the open magnetic field along the corridor. Squashing factor Q -maps of the large-scale topology further confirm super-radial expansion in support of the S-web theory for the slow wind. The thin corridor of upflows is identified as the source region of a slow solar wind stream characterized by ∼300 km s ^−1 velocities, low proton temperatures of ∼5 eV, extremely high density >100 cm ^−3 , and a short interval of moderate Alfvénicity accompanied by switchback events. When the connectivity changes from the corridor to the eastern side of the AR, the in situ plasma parameters of the slow solar wind indicate a distinctly different source region. These observations provide strong evidence that the narrow open-field corridors, forming part of the S-web, produce some extreme properties in their associated solar wind streams.

Nontypeable Haemophilus influenzae (NTHi) is a significant pathogen in respiratory disease and otitis media. Important for NTHi survival, colonization and persistence in vivo is the Sap (sensitivity to antimicrobial peptides) ABC transporter system. Current models propose a direct role for Sap in heme and antimicrobial peptide (AMP) transport. Here, the crystal structure of SapA, the periplasmic component of Sap, in a closed, ligand bound conformation, is presented. Phylogenetic and cavity volume analysis predicts that the small, hydrophobic SapA central ligand binding cavity is most likely occupied by a hydrophobic di- or tri- peptide. The cavity is of insufficient volume to accommodate heme or folded AMPs. Crystal structures of SapA have identified surface interactions with heme and dsRNA. Heme binds SapA weakly (Kd 282 μM) through a surface exposed histidine, while the dsRNA is coordinated via residues which constitute part of a conserved motif (estimated Kd 4.4 μM). The RNA affinity falls within the range observed for characterized RNA/protein complexes. Overall, we describe in molecular-detail the interactions of SapA with heme and dsRNA and propose a role for SapA in the transport of di- or tri-peptides.

The development of knowledge of how the coronal origin of the solar wind affects its in situ properties is one of the keys to understanding the relationship between the Sun and the heliosphere. In this paper, we analyse ACE/SWICS and WIND/3DP data spanning > 12 years, and test properties of solar wind suprathermal electron distributions for the presence of signatures of the coronal temperature at their origin which may remain at 1 AU. In particular we re-examine a previous suggestion that these properties correlate with the oxygen charge state ratio O7+ ∕ O6+, an established proxy for coronal electron temperature. We find only a very weak but variable correlation between measures of suprathermal electron energy content and O7+ ∕ O6+. The weak nature of the correlation leads us to conclude, in contrast to earlier results, that an initial relationship with core electron temperature has the possibility to exist in the corona, but that in most cases no strong signatures remain in the suprathermal electron distributions at 1 AU. It cannot yet be confirmed whether this is due to the effects of coronal conditions on the establishment of this relationship or due to the altering of the electron distributions by processing during transport in the solar wind en route to 1 AU. Contrasting results for the halo and strahl population favours the latter interpretation. Confirmation of this will be possible using Solar Orbiter data (cruise and nominal mission phase) to test whether the weakness of the relationship persists over a range of heliocentric distances. If the correlation is found to strengthen when closer to the Sun, then this would indicate an initial relationship which is being degraded, perhaps by wave–particle interactions, en route to the observer.

The mucus layer is an important physical niche within the gut which harbours a distinct microbial community. Here the authors show that specific carbohydrate-binding modules associated with bacterial carbohydrate-active enzymes are mucus adhesins that target regions of the distal colon rich in sialomucins.

Recent studies have shown that the ambient plasma in the near-Earth magnetotail can be compressed by the arrival of a dipolarization front (DF). In this paper we study the variations in the characteristics of currents flowing in this compressed region ahead of the DF, particularly the changes in the cross-tail current, using observations from the THEMIS satellites. Since we do not know whether the changes in the cross-tail current lead to a field-aligned current formation or just form a current loop in the magnetosphere, we thus use redistribution to represent these changes of local current density. We found that (1) the redistribution of the cross-tail current is a common feature preceding DFs; (2) the redistribution of cross-tail current is caused by plasma pressure gradient ahead of the DF and (3) the resultant net current redistributed by a DF is an order of magnitude smaller than the typical total current associated with a moderate substorm current wedge (SCW). Moreover, our results also suggest that the redistributed current ahead of the DF is closed by currents on the DF itself, forming a closed current loop around peaks in plasma pressure, what is traditionally referred to as a banana current.

Fragmento ABSTRACTO. Se comparó el metabolismo del diyodobenzoato marcado con 131I en las posiciones 3 y 5, y el de la tiroxina (T4) marcada en posiciones 3' y 5'. Este estudio se hizo usando perfusiones de hígado aislado de rata y además, ratas con fístula biliar. Después de la administración de la BHDB, se encontró que la desaparición de la radiactividad en la sangre fué mayor que cuando se administró T4. De !a misma manera, la excreción biliar de compuestos radiactivos fué mayor y la acumulación 131I en el hígado fué menor cuando se administró BHDB.

Flux transfer events (FTEs) are signatures of transient reconnection at the dayside magnetopause, transporting flux from the dayside of the magnetosphere into the magnetotail lobes. They have previously been observed to contain a combination of magnetosheath and magnetospheric plasma. On 12 February 2007, the four Cluster spacecraft were widely separated across the magnetopause and observed a crater-like FTE as they crossed the Earth's dayside magnetopause through its low-latitude boundary layer. The particle instruments on the Cluster spacecraft were in burst mode and returning data providing 3-D velocity distribution functions (VDFs) at 4 s resolution during the observation of this FTE. Moreover, the magnetic field observed during the event remained closely aligned with the spacecraft spin axis and thus we have been able to use these 3-D data to reconstruct nearly full pitch angle distributions of electrons and ions at high time resolution (up to 32 times faster than available from the normal mode data stream). These observations within the boundary layer and inside the core of the FTE show that both the interior and the surrounding structure of the FTE consist of multiple individual layers of plasma, in greater number than previously identified. Our observations show a cold plasma inside the core, a thin layer of antiparallel-moving electrons at the edge of FTE itself, and field-aligned ions with Alfvénic speeds at the trailing edge of the FTE. We discuss the plasma characteristics in these FTE layers, their possible relevance to the magnetopause reconnection processes and attempt to distinguish which of the various different FTE models may be relevant in this case. These data are particularly relevant given the impending launch of NASA's MMS mission, for which similar observations are expected to be more routine.

Travelling compression regions (TCRs) are perturbations in the magnetotail lobe magnetic field caused by structures moving Earthward or tailward within the plasma sheet. Previous works have suggested that these structures are created by either time-dependant reconnection occurring at a single X-line, forming a flux-bulge-type structure, or space-variant reconnection at multiple X-lines, forming flux-rope-type structures. In this study we examine an event in which Cluster 2 observed a TCR while the 3 remaining Cluster spacecraft observed the underlying magnetic structure at a range of distances from the neutral sheet. The magnetic structure has a velocity of (99, 154, −31) km s−1 in GSM (|V| = 186 km s−1), an estimated size of 1.19 RE along the direction of travel and a size between 1.94 and 2.86 RE in the direction perpendicular to the current sheet. As the structure passes the spacecraft, Cluster 1 and Cluster 4 observed a bipolar signature in BZ, plasma-sheet-like plasma and field-aligned electron flows. Cluster 3 passed closest to the centre of the structure and observed two separate reductions in the plasma density (with field-aligned electron flows); these drop-outs in the plasma sheet were possibly created by the actions of X-lines. The second drop-out in the plasma sheet also includes a reversal of the ion flow, a signature consistent with the passage of a reconnecting X-line past the spacecraft. Between the X-lines, the plasma outflow from the X-lines caused an increase in pressure which led to a localised expansion of the plasma and also the observations at Cluster 1 and Cluster 4 and the TCR. Our observations do not uniquely match either of the flux rope or the flux bulge predictions although the observation of two plasma sheet drop-outs (interpreted as X-lines, one active, one dormant) with plasma-sheet-like between them and only one TCR is a situation expected in multiple X-line reconnection.

During the late evening and night of 14 September 2004, the nightside auroral oval shows a distinct double oval configuration for several hours after a substorm onset at ~18:45 UT. This structure is observed both by the IMAGE satellite optical instruments focusing on the Southern Hemisphere, and by the MIRACLE ground-based instrument network in Scandinavia. At ~21:17 UT during the recovery phase of the substorm, an auroral streamer is detected by these instruments and the EISCAT radar, while simultaneously the Cluster satellites observe a bursty bulk flow in the conjugate portion of the plasma sheet in the magnetotail. Our combined data analysis reveals significant differences between the ionospheric equivalent current signature of this streamer within a double oval configuration, as compared to previously studied streamer events without such a configuration. We attribute these differences to the presence of an additional poleward polarization electric field between the poleward and the equatorward portions of the double oval, and show with a simple model that such an assumption can conceptually explain the observations. Further, we estimate the total current transferred in meridional direction by this recovery phase streamer to ~80 kA, significantly less than for previously analysed expansion phase streamer events. Both results indicate that the development of auroral streamers is dependent on the ambient background conditions in the magnetosphere-ionosphere system. The auroral streamer event studied was simultaneously observed in the conjugate Northern and Southern Hemisphere ionosphere.

Using data from the four Cluster spacecraft we study the separatrix regions of magnetic reconnection sites at the dayside magnetopause under conditions when reconnection is occurring in the magnetopause current layer which separates magnetosheath plasma from the hot magnetospheric plasma sheet. We define the separatrix region as the region between the separatrix – the first field line opened by reconnection – and the reconnection jet (outflow region). We analyze eight separatrix region crossings on the magnetospheric side of the magnetopause and present detailed data for two of the events. We show that characteristic widths of the separatrix regions are of the order of ten ion inertial lengths at the magnetopause. Narrow separatrix regions with widths comparable to a few ion inertial lengths are rare. We show that inside the separatrix region there is a density cavity which sometimes has complex internal structure with multiple density dips. Strong electric fields exist inside the separatrix regions and the electric potential drop across the regions can be up to several kV. On the magnetosheath side of the region there is a density gradient with strong field aligned currents. The observed strong electric fields and currents inside the separatrix region can be important for a local energization of ions and electrons, particularly of ionospheric origin, as well as for magnetosphere-ionosphere coupling.

On 13 August 2002, during a substorm, Cluster encountered two earthward moving flux ropes (FR) in the central magnetotail. The first FR was observed during the expansion phase of the substorm, and the second FR during the recovery phase. In the conjugate ionospheric region in Northern Fennoscandia, the ionospheric equivalent currents were observed by the MIRACLE network and the auroral evolution was monitored by the Wideband Imaging Camera (WIC) on-board the IMAGE satellite. Extending the study of Amm et al. (2006), we examine and compare the possible ionospheric signatures associated with the two FRs. Amm et al. studied the first event in detail and found that the ionospheric footprint of Cluster coincided with a region of downward field-aligned current. They suggested that this region of downward current, together with a trailing region of upward current further southwestward, might correspond to the ends of the FR. Unlike during the first FR, however, we do not see any clear ionospheric features associated with the second one. In the GSM xy-plane, the first flux rope axis was tilted with respect to the y-direction by 29°, while the second flux rope axis was almost aligned in the y-direction, with an angle of 4° only. It is possible that due to the length and orientation of the second FR, any ionospheric signatures were simply mapped outside the region covered by the ground-based instruments. We suggest that the ground signatures of a FR depend on the orientation and the length of the structure.

Using Advanced Composition Explorer (ACE) in situ data we identify and describe an interplanetary magnetic cloud (MC) observed near Earth on 13 April 2006. We also use multi-instrument and multi-wavelength observations from the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE) and ground-based solar observatories to determine the solar source of this magnetic cloud. A launch window for the MC between 9 and 11 April 2006 was estimated from the propagation time of the ejecta observed near Earth. A number of large active regions (ARs) were present on the Sun during this period, which were initially considered to be the most likely candidate source regions of the MC. However, it was determined that the solar source of the MC was a small, spotless active region observed in the Northern Hemisphere. Following an eruption from this region on 11 April 2006, the ACE spacecraft detected, 59 h later, the passage of the MC, preceded by the arrival of a weak, forward fast shock. The link between the eruption in this active region and the interplanetary MC is supported by several pieces of evidence, including the location of the solar source near to the disk centre and to the east of the central meridian (in agreement with the spacecraft trajectory through the western leg of the magnetic cloud), the propagation time of the ejecta, the agreement between the amount of flux in the magnetic cloud and in the active region, and the agreement between the signs of helicity of the magnetic cloud and the active region (which differs from the sign of helicity of each of the other active regions on the Sun at this time). In addition, the active region is located on the boundary of a coronal hole, and a high speed solar wind stream originating from this region is observed near Earth shortly after the passage of the magnetic cloud.

The magnetopause (MP) reconnection is characterized by a density asymmetry across the current sheet. The asymmetry is expected to produce characteristic features in the reconnection layer. Here we present a comparison between the Cluster MP crossing reported by Retinò et al. (2006) and virtual observations in two-dimensional particle-in-cell simulation results. The simulation, which includes the density asymmetry but has zero guide field in the initial condition, has reproduced well the observed features as follows: (1) The prominent density dip region is detected at the separatrix region (SR) on the magnetospheric (MSP) side of the MP. (2) The intense electric field normal to the MP is pointing to the center of the MP at the location where the density dip is detected. (3) The ion bulk outflow due to the magnetic reconnection is seen to be biased towards the MSP side. (4) The out-of-plane magnetic field (the Hall magnetic field) has bipolar rather than quadrupolar structure, the latter of which is seen for a density symmetric case. The simulation also showed rich electron dynamics (formation of field-aligned beams) in the proximity of the separatrices, which was not fully resolved in the observations. Stepping beyond the simulation-observation comparison, we have also analyzed the electron acceleration and the field line structure in the simulation results. It is found that the bipolar Hall magnetic field structure is produced by the substantial drift of the reconnected field lines at the MSP SR due to the enhanced normal electric field. The field-aligned electrons at the same MSP SR are identified as the gun smokes of the electron acceleration in the close proximity of the X-line. We have also analyzed the X-line structure obtained in the simulation to find that the density asymmetry leads to a steep density gradient in the in-flow region, which may lead to a non-stationary behavior of the X-line when three-dimensional freedom is taken into account.

Many phenomena in the Earth's magnetotail have characteristic temporal scales of several minutes and spatial scales of a few Earth radii (RE). Examples of such transient and localized mesoscale phenomena are bursty bulk flows, beamlets, energy dispersed ion beams, flux ropes, traveling compression regions, night-side flux transfer events, and rapid flappings of the current sheet. Although most of these observations are linked to specific interpretations or theoretical models they are inter-related and can be the different aspects of a physical process or origin. Recognizing the inter-connected nature of the different transient and localized phenomena in the magnetotail, this paper reviews their observations by highlighting their important characteristics, with emphasis on the new results from Cluster multipoint observations. The multi-point Cluster measurements have provided, for the first time, the ability to distinguish between temporal and spatial variations, and to resolve spatial structures. Some examples of the new results are: flux ropes with widths of 0.3 RE, transient field aligned currents associated with bursty bulk flows and connected to the Hall current at the magnetic reconnection, flappings of the magnetotail current sheet with time scales of 100 s–10 min and thickness of few thousand km, and particle energization including velocity and time dispersed ion structures with the latter having durations of 1–3 min. The current theories of these transient and localized processes are based largely on magnetic reconnection, although the important role of the interchange and other plasma modes are now well recognized. On the kinetic scale, the energization of particles takes place near the magnetic X-point by non-adiabatic processes and wave-particle interactions. The theory, modeling and simulations of the plasma and field signatures are reviewed and the links among the different observational concepts and the theoretical frameworks are discussed. The mesoscale processes in the magnetotail and the strong coupling among them are crucial in developing a comprehensive understanding of the multiscale phenomena of the magnetosphere.