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This study reports on the physical properties and geochemistry of aeolian bedform grains along the Curiosity rover traverse in Gale crater from Vera Rubin Ridge to the Sands of Forvie (Sols 1902–2995), and includes comparisons to results made earlier in the mission. Volumetrically, <150 μm grains dominate active aeolian bedforms in the study area, similar to previous findings elsewhere at Gale crater and at other locations on Mars. Coarser grains, up to 2.9 mm long, are present on larger active bedforms. The larger 1–3 mm active grains commonly are reddish or whitish in color and irregular in shape, suggesting erosion of local bedrock as sources. One inactive megaripple had a surface of dust‐covered 2–15 mm grains, with smaller <150 μm grains between and within the bedform interior. Geochemical measurements show element concentrations vary according to position on the bedform, sand activity, and grain contributions from local bedrock. A strong positive correlation between Mg and Ni is identified on active bedform surfaces, with the highest Ni always corresponding to ripple crests where the coarsest gray and clear grains were commonly found. There is also a correlation between Ti and Cr for the majority of active sands, with the finer active sands in ripple troughs and sand patches having the greatest number of red grains and highest Cr concentrations. These results show the smaller scale physical properties and geochemistry of several types of aeolian bedforms on Mars formed under current and ancient environments. Plain Language Summary: This work reports sand grain characteristics of Martian aeolian bedforms along the traverse of NASA's Mars Science Laboratory "Curiosity" rover at Gale crater from Sols 1902–2995 of its mission, and compares their characteristics to previous measurements of aeolian ripple sands on Mars. Large, active ripples have larger grains on their crests and flanks compared to smaller active ripples. Compositional variations among these grains correlate with the grain color and size. Some coarse grains on the larger active ripples are lithic fragments derived from either local Murray bedrock or from basalts. Finer grains are characteristic of smaller ripples and trough areas between large ripple crests. These finer grains are redder in color than coarser grains on larger ripples. The rover examined an inactive megaripple, which was found to be covered by coarser grains 0.3–11 mm that could have been eroded from local bedrock. Compositional differences among aeolian ripples may reflect how much of their surfaces are comprised of coarser grains that either are more resistant to erosion or are locally derived, compared with finer grains. These results provide insight into the characteristics of Martian aeolian ripples at much higher resolution than possible from orbital observations. Key Points: Larger ripples have a higher abundance of coarser gray grains compared to smaller ripples, ripple troughs, and sand patchesThe Ni concentration increases and the Cr concentration decreases as the abundance of gray grains on the ripple increasesInactive bedforms have an armor of coarse grains that can be pebbles and granules sourced from the local bedrock [ABSTRACT FROM AUTHOR]

On Mars, near the equator, much of the terrain in Gale Crater consists of bedrock outcrops separated by relatively smooth, uniform regolith surfaces. In scattered sites, however, distinct patterns—in the form and texture of the ground surface—contrast sharply with the typical terrain and with eolian bedforms. This paper focuses on these diverse, intriguing ground patterns. They include ∼1 to >10 m‐long linear disruptions of uniform regolith surfaces, alignments, and other arrangements of similar‐sized rock fragments and shallow, ∼0.1 m‐wide sandy troughs 1–10 m in length. Similar features were recognized early in the Mars Science Laboratory (MSL) mission, but they received only limited attention until Curiosity, the MSL rover, encountered striking examples in the Glen Torridon region. Herein, the ground patterns are illustrated with rover images. Potential mechanisms are briefly discussed in the context of the bedrock composition and atmospheric conditions documented by Curiosity. The evidence suggests that the patterns are active forms of spontaneous granular organization. It leads to the hypothesis that the patterns arise and develop from miniscule, inferred cyclic expansion and contraction of the bedrock and regolith, likely driven by oscillating transfers of energy and moisture between the atmosphere and the terrain. The hypothesis has significant implications for studies of contemporary processes on Mars on both sides of the atmosphere‐lithosphere interface. The ground patterns, as well as ripples and dunes formed by the wind, constitute remarkable extra‐terrestrial examples of granular self‐organization, complex phenomena well known in diverse systems on Earth. Plain Language Summary: Gale crater, which is near Mars' equator (4.5°S latitude), is generally rocky with sand and rocks scattered between extensive bedrock exposures. However, in a few local sites, distinct natural patterns mark the ground with ∼0.1 m‐wide, sand‐lined troughs and rocks arranged geometrically. We use detailed images from Curiosity, the Mars Science Laboratory rover, to illustrate these intriguing patterns in the Glen Torridon area, where they are widespread. We suggest they are currently active in the dry rock debris at the surface and driven by the sustained shrink‐swell activity of the underlying bedrock. This inferred activity, which likely results from variations in moisture and temperature in the lower Mars atmosphere, could generate these ground patterns, much like vibrations or analogous cyclic disturbances cause patterns to form naturally in diverse settings with granular materials of different sizes and shapes. The inferred cyclic shrink‐swell behavior of the shallow subsurface and underlying transfers of energy and mass may be of broad interest because of their potential implications for studies of processes shaping the Mars landscape and occurring in the lower atmosphere. These ground features, as well as ripples and dunes formed by the wind, are visible examples of extra‐terrestrial self‐organization. Key Points: Near Mars' equator, sandy troughs and organized rock fragments locally form distinct patterns suggestive of active ground deformationUnlike patterned ground on Earth, the ground patterns in Gale Crater form in thin, dry regolith overlying jointed bedrockAtmosphere‐surface exchange of energy and water vapor is inferred to drive self‐organization through cyclic subsurface volume changes [ABSTRACT FROM AUTHOR]

Inositol 1,4,5-trisphosphate receptors (IP3Rs) initiate a diverse array of physiological responses by carefully orchestrating intracellular calcium (Ca2+) signals in response to various external cues. Notably, IP3R channel activity is determined by several obligatory factors, including IP3, Ca2+, and ATP. The critical basic amino acid residues in the N-terminal IP3-binding core (IBC) region that facilitate IP3 binding are well characterized. In contrast, the residues conferring regulation by Ca2+ have yet to be ascertained. Using comparative structural analysis of Ca2+-binding sites identified in two main families of intracellular Ca2+-release channels, ryanodine receptors (RyRs) and IP3Rs, we identified putative acidic residues coordinating Ca2+ in the cytosolic calcium sensor region in IP3Rs. We determined the consequences of substituting putative Ca2+ binding, acidic residues in IP3R family members. We show that the agonist-induced Ca2+ release, single-channel open probability (P0), and Ca2+ sensitivities are markedly altered when the negative charge on the conserved acidic side chain residues is neutralized. Remarkably, neutralizing the negatively charged side chain on two of the residues individually in the putative Ca2+-binding pocket shifted the Ca2+ required to activate IP3R to higher concentrations, indicating that these residues likely are a component of the Ca2+ activation site in IP3R. Taken together, our findings indicate that Ca2+ binding to a well-conserved activation site is a common underlying mechanism resulting in increased channel activity shared by IP3Rs and RyRs. [ABSTRACT FROM AUTHOR]

Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of regularly spaced, curvilinear, and sometimes branching bedrock ridges that occur within the Glen Torridon region on the lower northwest flank of Aeolis Mons, the central mound within Gale crater. During Curiosity's exploration of Glen Torridon between sols ∼2300–3080, the rover drove through this field of ridges, providing the opportunity for in situ observation of these features. This study uses orbiter and rover data to characterize ridge morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, we find that the Glen Torridon ridges are consistent with an origin as wind‐eroded bedrock ridges, carved during the exhumation of Mount Sharp. Erosional features like the Glen Torridon ridges observed elsewhere on Mars, termed periodic bedrock ridges (PBRs), have been interpreted to form transverse to the dominant wind direction. The size and morphology of the Glen Torridon PBRs are consistent with transverse formative winds, but the orientation of nearby aeolian bedforms and bedrock erosional features raise the possibility of PBR formation by a net northeasterly wind regime. Although several formation models for the Glen Torridon PBRs are still under consideration, and questions persist about the nature of PBR‐forming paleowinds, the presence of PBRs at this site provides important constraints on the depositional and erosional history of Gale crater. Plain Language Summary: Wind has played a major role in sculpting the surface of Mars. Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover since it landed there in 2012, contains a vast and varied record of deposition and erosion by the wind. This study focuses on a series of regularly spaced, generally straight bedrock ridges that occur within the clay‐bearing Glen Torridon region of Aeolis Mons (informally named Mount Sharp) in Gale crater. During Curiosity's exploration of the Glen Torridon region between sols ∼2300–3080 of the mission, the rover drove through this field of ridges, acquiring images and compositional observations along the way. This study characterizes the Glen Torridon ridges using orbiter and rover data to determine their shape, size, occurrence, and relationship to other wind‐formed features in the area. We find that the Glen Torridon ridges were carved by wind into the bedrock of Mount Sharp. Questions remain about the winds that formed these ridges, but this study provides important information about the history and environment of Gale crater and reports the first rover observations of this type of erosional feature on Mars. Key Points: Decameter‐long, regularly spaced bedrock ridges oriented northeast‐southwest occur throughout the Glen Torridon region of Aeolis MonsGlen Torridon ridges cross‐cut elevation contours and bedding, exhibit bifurcations, and are disrupted by small impact cratersGlen Torridon ridges are erosional periodic bedrock ridges whose formation places erosional and depositional constraints on Aeolis Mons [ABSTRACT FROM AUTHOR]

A suite of high resolution cameras onboard the Mars Science Laboratory (MSL) Curiosity rover have provided an unparalleled look at active aeolian processes on Mars, including within the first active dune field explored on another planet, the Bagnold Dunes. Here we present results from a subset of MSL's repeat imaging ("change detection") experiments with temporal resolutions sufficient to probe the diurnal variability in winds within Gale crater. Images reveal that saltation is a near‐daily phenomenon during southern summer, with repeatable diurnal circulation patterns producing steady impact ripple migration toward the west/southwest. Nighttime fluxes are inferred to be ∼four times larger than daytime fluxes, consistent with predictions from the MarsWRF model of multiple periods of enhanced wind between sunset and sunrise. Multiple factors are likely facilitating saltation at this time: (a) time‐averaged nighttime winds have a higher degree of variance (i.e., higher peak friction speeds) than daytime winds, (b) interactions between regional Hadley flows and local, thermally driven slope winds cause increased turbulence at night, and (c) relatively higher atmospheric density produces correspondingly higher shear stresses and decreases critical thresholds. Observations of sand transport at a range of spatiotemporal scales (down to scale of individual particles moving on the timescale of seconds) support the idea that bedform migration is driven by intermittent, low‐flux saltation events when winds fluctuate between canonical impact and fluid thresholds. Yet, whereas gustiness may play a role in initiating transport, saltation is found to be highly predictable on diurnal timescales and is only stochastic on the shortest timescales characteristic of turbulent fluctuations in wind. Plain Language Summary: Repeat "change detection" imaging experiments performed using cameras onboard the Mars Science Laboratory Curiosity rover have provided a rare look at active wind‐blown sand movement on Mars. Rover images acquired during local summer reveal near‐daily migration of sand ripples toward the west/southwest. Ripple migration is inferred to occur predominately between sunset and sunrise each sol, based on the observation of ∼four times more sand transport at night than during the day. In lieu of in situ meteorological data, predictions from the MarsWRF atmospheric model are used to interpret the circulation patterns responsible for sand transport. Close comparison between the model and observations suggests that dunes and ripples in the vicinity of the rover's traverse are being shaped by a unique combination of regional circulation patterns and local slope winds. Close examination of sand movement (down to the scale of individual sand grains) helps shed light on the physics of sand transport under natural Martian conditions and decipher possible differences between wind‐driven landscape modification on Earth and Mars. Key Points: Curiosity rover images have enabled the examination of aeolian transport on smaller spatiotemporal scales than achieved previously on MarsRecurring nighttime circulation patterns generate near‐daily impact ripple migration along the rover's traverse during local summerRipple morphodynamics are consistent with intermittent, low‐flux saltation driven by winds between traditional impact and fluid thresholds [ABSTRACT FROM AUTHOR]

Type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) is the predominant Ca2+-release channel in neurons. IP3R1 mediates Ca2+ release from the endoplasmic reticulum into the cytosol and thereby is involved in many physiological processes. Here, we present the cryo-EM structures of full-length rat IP3R1 reconstituted in lipid nanodisc and detergent solubilized in the presence of phosphatidylcholine determined in ligand-free, closed states by single-particle electron cryo-microscopy. Notably, both structures exhibit the well-established IP3R1 protein fold and reveal a nearly complete representation of lipids with similar locations of ordered lipids bound to the transmembrane domains. The lipid-bound structures show improved features that enabled us to unambiguously build atomic models of IP3R1 including two membrane associated helices that were not previously resolved in the TM region. Our findings suggest conserved locations of protein-bound lipids among homotetrameric ion channels that are critical for their structural and functional integrity despite the diversity of structural mechanisms for their gating. 3D structure of full-length rat type 1 inositol 1,4,5-trisphosphate receptor reconstituted in lipid nanodisc is determined using single-particle cryo-electron microscopy. The study suggests conserved locations of protein-bound lipids among structurally diverse, homo-tetrameric ion channels. [ABSTRACT FROM AUTHOR]

The InSight mission landed its scientific payload in Homestead hollow, a quasi‐circular depression interpreted to be a highly degraded impact crater that is 27 m in diameter. The original pristine crater formed in a preexisting impact‐generated regolith averaging ~3 m thick and the surrounding ejecta deposit, consisting of coarse and mostly fine fragments, was in disequilibrium with local geomorphic thresholds. As a result, early, relatively rapid degradation by mostly eolian, and lesser impact processes and mass‐wasting, stripped the rim and mostly infilled the hollow where sediments were sequestered. Early, faster degradation during the first ~0.1 Ga was followed by much slower degradation over the bulk of the 0.4–0.7 Ga history of the crater. Pulses of much lesser degradation are attributed to impacts in and nearby the hollow, which emplaced some rocks as ejecta and provided small inventories of fine sediments for limited additional infilling. Even lesser sediments were derived from the very slow production of fines via weathering of resistant basaltic rocks. Nevertheless, indurated regolith caps the sediment fill within the hollow and creates a relatively stable present‐day surface that further sequesters infilling sediments from remobilization. The degradation sequence at Homestead hollow is like that established at the Spirit rover landing site in Gusev crater and points to the importance of eolian, and lesser impact and mass‐wasting processes, in degrading volcanic surfaces on Mars over the past ~1 Ga. Plain Language Summary: The InSight mission landed in a highly degraded impact crater dubbed Homestead hollow in Elysium Planitia on Mars. The hollow interior is quite flat and smooth, and mostly infilled by fine‐grained sediments. Rocks are 2–3 times more numerous on the western side dubbed Rocky Field. The hollow lacks a raised rim but is marked by an increase in larger rocks. The distribution of windblown and impact materials within, around, and local to the hollow indicate degradation was mostly by wind stripping of fines from the rim and depositing them inside the hollow, with lesser contributions from impact and mass wasting processes. Rocky Field was likely formed by emplacement of ejecta during a nearby impact event occurring relatively soon after Homestead hollow formed. Most degradation occurred during the first ~0.1 Ga after hollow formation. Limited modification over most of hollow history was associated with small pulses of infilling and rock emplacement during/following nearby impact events and very slow weathering of basaltic rocks. Degradation at Homestead hollow is similar to the modification of small craters at the Spirit landing site in Gusev crater, which shows common geomorphic processes occurred on comparable surfaces in different places on Mars during the last ~1 Ga. Key Points: Homestead hollow is a degraded impact crater that was modified by mostly eolian and lesser impact and mass‐wasting processesRocks on the western side of the hollow are ejecta emplaced during the formation of a nearby crater relatively early in hollow historyMost hollow degradation occurred during the first ~0.1 Ga after formation, followed by limited exterior stripping and interior infilling [ABSTRACT FROM AUTHOR]

We measured sand sizes and shapes on diverse eolian bedforms in Gale crater to help constrain models of eolian sediment transport on Mars. All grains are subangular to rounded with circularities of ~0.93–0.97, indicating an extensive abrasion history. There are two types of active bedforms based on grain size: (1) ripples composed of 50‐ to 150‐μm grains and (2) ripples that also include 250‐ to 500‐μm grains along their crests, in some cases with small amounts of even coarser grains (up to 1.4 mm). The smallest grain sizes (50–150 μm) are volumetrically the most abundant at all active bedforms. Inactive bedforms have surfaces of 350‐ to 2,000‐μm grains with finer‐grained interiors, consistent with observations made by rovers at other landing sites. Grains coarser than ~300 μm are less prone to mobilization driven by smaller saltating grains, making bedforms with concentrations of coarser grains more susceptible to surface stabilization and inactivity. Plain Language Summary: We used microscopic images taken by a camera on the Curiosity rover at Mars to measure the shapes and sizes of sand grains. There are two types of active ripples that we identified based upon grain size: those that have grain sizes between 50 and 150 microns and those with coarser grains between 250 and 500 microns. Most of the grains on the active Bagnold dunes are very fine sand, except at the crests of larger ripples where the grains tend to be larger. The grains are circular and rounded, indicating that they have experienced an extensive abrasion history. Inactive ripples have coarser grains (350–2,000 μm) armoring finer interior grains, some of which could be locally derived from the Stimson sandstone and Murray Formation outcrops. On Earth, the physical properties of grains partly control bedform morphology and are closely linked with mobility. Because these same principles are expected on Mars, it is important to know sand grain size and shape distributed across diverse ripple morphologies to help constrain models of martian bedform formation. Key Points: Sand grains on eolian bedforms on Mars vary in size and shape depending upon whether the bedform is active or inactiveThe size distribution of most active sands is narrow and very fine (50‐150 micrometers) unless on a coarse‐grained (250‐500 micrometers size) rippleCoarse‐grained ripples at Gale have similar grain sizes to those at both Gusev crater and Meridiani Planum landing sites [ABSTRACT FROM AUTHOR]

Abstract: Orbiter‐based observations have demonstrated that active aeolian environments are ubiquitous across Mars. Here we examine one such environment, the Bagnold Dune Field in Gale crater, with repeat imaging campaigns conducted from Curiosity during southern summer. Images reveal widespread migration of aeolian impact ripples (up to 2.8 cm/sol), which is in stark contrast to the inactivity of similar bedforms during southern winter. The winds responsible for steady southwestward migration of ripples are consistent with predictions of regional‐scale flows that enter the crater from the north and interact with the topography of Mount Sharp but are not fully representative of all dune‐forming winds. Inferred friction speeds of 1.5 m/s needed to explain mobilization of bedforms are likely not being achieved, and thus, a majority of sediment transport may be taking place at subthreshold conditions. This hypothesis is further supported by sand flux estimates that suggest a low saltation flux environment within the dune field. [ABSTRACT FROM AUTHOR]

Inositol-1,4,5-trisphosphate receptors (InsP3Rs) are ubiquitous ion channels responsible for cytosolic Ca2+ signalling and essential for a broad array of cellular processes ranging from contraction to secretion, and from proliferation to cell death. Despite decades of research on InsP3Rs, a mechanistic understanding of their structure-function relationship is lacking. Here we present the first, to our knowledge, near-atomic (4.7 Å) resolution electron cryomicroscopy structure of the tetrameric mammalian type 1 InsP3R channel in its apo-state. At this resolution, we are able to trace unambiguously ∼85% of the protein backbone, allowing us to identify the structural elements involved in gating and modulation of this 1.3-megadalton channel. Although the central Ca2+-conduction pathway is similar to other ion channels, including the closely related randiness receptor, the cytosolic carboxy termini are uniquely arranged in a left-handed α-helical bundle, directly interacting with the amino-terminal domains of adjacent subunits. This configuration suggests a molecular mechanism for allosteric regulation of channel gating by intracellular signals. [ABSTRACT FROM AUTHOR]

Ryanodine receptors (RyRs) are tetrameric ligand-gated Ca2+ release channels that are responsible for the increase of cytosolic Ca2+ concentration leading to muscle contraction. Our current understanding of RyR channel gating and regulation is greatly limited due to the lack of a high-resolution structure of the channel protein. The enormous size and unwieldy shape of Ca2+ release channels make X-ray or NMR methods difficult to apply for high-resolution structural analysis of the full-length functional channel. Single-particle electron cryomicroscopy (cryo-EM) is one of the only effective techniques for the study of such a large integral membrane protein and its molecular interactions. Despite recent developments in cryo- EM technologies and break-through single-particle cryo-EM studies of ion channels, cryospecimen preparation, particularly the presence of detergent in the buffer, remains the main impediment to obtaining atomic-resolution structures of ion channels and a multitude of other integral membrane protein complexes. In this review we will discuss properties of several detergents that have been successfully utilized in cryo-EM studies of ion channels and the emergence of the detergent alternative amphipol to stabilize ion channels for structurefunction characterization. Future structural studies of challenging specimen like ion channels are likely to be facilitated by cryo-EM amenable detergents or alternative surfactants. [ABSTRACT FROM AUTHOR]

ATP is an important modulator of gating in type 1 ryanodine receptor (RyR1), also known as a Ca2+ release channel in skeletal muscle cells.The activating effect of ATP on this channel is achieved by directly binding to one or more sites on the RyR1 protein. However, the number and location of these sites have yet to be determined.To identify the ATP-binding regions within RyR1 we used 2N3ATP-2', 3'-Biotin-LC-Hydrazone (BioATP-HDZ),a photo-reactive ATP analog to covalently label the channel. We found that BioATP-HDZ binds RyR1 specifically with an IC50 = 0.6±0.2 mM, comparable with the reported EC50 for activation of RyR1 with ATP.Controlled proteolysis of labeled RyR1 followed by sequence analysis revealed three fragments with apparent molecular masses of 95, 45 and 70 kDa that were crosslinked by BioATP-HDZ and identified as RyR1 sequences. Our analysis identified four glycine-rich consensus motifs that can potentially constitute ATPbinding sites and are located within the N-terminal 95-kDa fragment. These putative nucleotide-binding sequences include amino acids 699-704, 701-706, 1081-1084 and 1195-1200, which are conserved among the three RyR isoforms. Located next to the N-terminal disease hotspot region in RyR1, these sequences may communicate the effects of ATP-binding to channel function by tuning conformational motions within the neighboring cytoplasmic regulatory domains. Two other labeled fragments lack ATP-binding consensus motifs and may form non-canonical ATP-binding sites. Based on domain topology in the 3D structure of RyR1 it is also conceivable that the identified ATP-binding regions, despite their wide separation in the primary sequence, may actually constitute the same non-contiguous ATP-binding pocket within the channel tetramer. [ABSTRACT FROM AUTHOR]

The complex interplay of proteins and other molecules, often in the form of large transitory assemblies, are critical to cellular function. Today, X-ray crystallography and electron cryo-microscopy (cryo-EM) are routinely used to image these macromolecular complexes, though often at limited resolutions. Despite the rapidly growing number of macromolecular structures, few tools exist for modeling and annotating structures in the range of 3-10 Å resolution. To address this need, we have developed a number of utilities specifically targeting subnanometer resolution density maps. As part of the 2010 Cryo-EM Modeling Challenge, we demonstrated two of our latest de novo modeling tools, Pathwalking and Gorgon, as well as a tool for secondary structure identification (SSEHunter) and a new rigid-body/flexible fitting tool in Gorgon. In total, we submitted 30 structural models from ten different subnanometer resolution data sets in four of the six challenge categories. Each of our utlities produced accurate structural models and annotations across the various density maps. In the end, the utilities that we present here offer users a robust toolkit for analyzing and modeling protein structure in macromolecular assemblies at non-atomic resolutions. © 2012 Wiley Periodicals, Inc. Biopolymers 97: 655-668, 2012. [ABSTRACT FROM AUTHOR]

Voltage-dependent calcium channels (Cay) open in response to changes in membrane potential, but their activity is modulated by Ca[sup2+] binding to calmodulin (CaM). Structural studies of this family of channels have focused on CaM bound to the IQ motif; however, the minimal differences between structures cannot adequately describe CaM's role in the regulation of these channels. We report a unique crystal structure of a 77-residue fragment of the Cavi .2 α1 subunit carboxyl terminus, which includes a tandem of the pre-IQ and lQ domains, in complex with Ca[sup2+] CaM in 2 distinct binding modes. The structure of the Cav1.2 fragment is an unusual dimer of 2 coiled-coiled pre-IQ regions bridged by 2 Ca[sup2+]CaMs interact- ing with the pre-lQ regions and a canonical Cav1-lQ-Ca[sup2+]CaM complex. Native Cav1.2 channels are shown to be a mixture of monomers/dimers and a point mutation in the pre-IQ region predicted to abolish the coiled-coil structure significantly reduces Ca[sup2+]-dependent inactivation of heterologously expressed Cav1.2 channels. [ABSTRACT FROM AUTHOR]