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Although Mycobacterium tuberculosis and related species are considered to be typical endosomal pathogens, recent studies have suggested that mycobacteria can be present in the cytoplasm of infected cells and cause cytoskeleton rearrangements, the mechanisms of which remain unknown. Here, we used single-molecule force spectroscopy to demonstrate that the heparin-binding hemagglutinin (HBHA), a surface adhesin from Mycobacterium tuberculosis displaying sequence similarities with actin-binding proteins, is able to bind to actin. Force curves recorded between actin and the coiled-coil, N-terminal domain of HBHA showed a bimodal distribution of binding forces reflecting the detection of single and double HBHA-actin interactions. Force curves obtained between actin and the lysine-rich C-terminal domain of HBHA showed a broader distribution of binding events, suggesting they originate primarily from intermolecular electrostatic bridges between cationic HBHA domains and anionic actin residues. We also explored the dynamics of the HBHA-actin interaction, showing that the binding force and binding frequency increased with the pulling speed and contact time, respectively. Taken together, our data indicate that HBHA is able to specifically bind actin, via both its N-terminal and C-terminal domains, strongly suggesting a role of the HBHA-actin interaction in the pathogenesis of mycobacterial diseases.

Several regulators are involved in the control of cell cycle progression in the bacterial model system Caulobacter crescentus, which divides asymmetrically into a vegetative G1-phase (swarmer) cell and a replicative S-phase (stalked) cell. Here we report a novel functional interaction between the enigmatic cell cycle regulator GcrA and the N6-adenosine methyltransferase CcrM, both highly conserved proteins among Alphaproteobacteria, that are activated early and at the end of S-phase, respectively. As no direct biochemical and regulatory relationship between GcrA and CcrM were known, we used a combination of ChIP (chromatin-immunoprecipitation), biochemical and biophysical experimentation, and genetics to show that GcrA is a dimeric DNA–binding protein that preferentially targets promoters harbouring CcrM methylation sites. After tracing CcrM-dependent N6-methyl-adenosine promoter marks at a genome-wide scale, we show that these marks recruit GcrA in vitro and in vivo. Moreover, we found that, in the presence of a methylated target, GcrA recruits the RNA polymerase to the promoter, consistent with its role in transcriptional activation. Since methylation-dependent DNA binding is also observed with GcrA orthologs from other Alphaproteobacteria, we conclude that GcrA is the founding member of a new and conserved class of transcriptional regulators that function as molecular effectors of a methylation-dependent (non-heritable) epigenetic switch that regulates gene expression during the cell cycle. [ABSTRACT FROM AUTHOR]

The Bug proteins form a large family of periplasmic solute-binding receptors present in a number of bacterial species. Here, the crystal structure of Bordetella pertussis BugE, a member of the Bug family coded by the gene BP0250, is reported. It adopts the Venus flytrap architecture of periplasmic binding proteins, with two domains separated by a deep cleft. BugE has a bound ligand, identified as a glutamate. The structure of B. pertussis BugD, which is an aspartic acid transporter, has recently been reported. These structures reveal high conservation of the Bug architecture, despite limited sequence identity. They share a common carboxylate-binding motif defined by two strand–β-turn–α-­helix motifs, also involving two water molecules to bridge the carboxylate O atoms to the protein. The two water molecules are hydrogen bonded to a common main-chain carbonyl group. Although the features of the carboxylate-binding motif are totally conserved, the ligand in BugE is bound by its side-chain carboxylate group rather than by its α-­carboxylate as in BugD. This specific ligand-binding motif is highly conserved in Bug proteins and the BugE structure suggests that the cavity of the Bug proteins might also accommodate carboxylated solutes other than amino acids. The vast expansion of the Bug family in several bacterial genera is likely to be explained by the possible diversity of ligands. No charged residues are involved in glutamate binding by BugE, unlike what has been described for all glutamate receptors reported so far. [ABSTRACT FROM AUTHOR]

DctP6 and DctP7 are two Bordetella pertussis proteins which belong to the extracytoplasmic solute receptors (ESR) superfamily. ESRs are involved in the transport of substrates from the periplasm to the cytosol of Gram-negative bacteria. DctP6 and DctP7 have been crystallized and diffraction data were collected using a synchrotron-radiation source. DctP6 crystallized in space group P41212, with unit-cell parameters a = 108.39, b = 108.39, c = 63.09 Å, while selenomethionyl-derivatized DctP7 crystallized in space group P212121, with unit-cell parameters a = 64.87, b = 149.83, c = 170.65 Å. The three-dimensional structure of DctP7 will be determined by single-wavelength anomalous diffraction, while the DctP6 structure will be solved by molecular-replacement methods. [ABSTRACT FROM AUTHOR]

The article provides information on the role of two starch-bound proteins, LESV and ESV1, in promoting the phase transition of amylopectin-like glucans, which are the main components of starch in plants. These proteins facilitate the alignment and crystallization of glucan double helices, leading to the formation of semi-crystalline granules.

Presents a corrective reprint of the article "Nanoscale mapping and functional analysis of individual adhesions on living bacteria," by Vincent Dupres, Franco D. Menozzi, Camille Locht, Brian H. Clare, Nicholas L. Abbott, Stephane Cuenot, Coralie Bompard, Dominique Raze and Yves F. Dufrene, published in the August 2005 issue of the journal "Nature Methods."

Starch-branching enzymes (BEs) are essential for starch synthesis in both plants and algae where they influence the architecture and physical properties of starch granules. Within Embryophytes, BEs are classified as type 1 and type 2 depending on their substrate preference. In this article, we report the characterization of the three BE isoforms encoded in the genome of the starch producing green algae Chlamydomonas reinhardtii : two type 2 BEs (BE2 and BE3) and a single type 1 BE (BE1). Using single mutant strains, we analyzed the consequences of the lack of each isoform on both transitory and storage starches. The transferred glucan substrate and the chain length specificities of each isoform were also determined. We show that only BE2 and BE3 isoforms are involved in starch synthesis and that, although both isoforms possess similar enzymatic properties, BE3 is critical for both transitory and storage starch metabolism. Finally, we propose putative explanations for the strong phenotype differences evidenced between the C. reinhardtii be2 and be3 mutants, including functional redundancy, enzymatic regulation or alterations in the composition of multimeric enzyme complexes., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Courseaux, George, Deschamps, Bompard, Duchêne and Dauvillée.)

Proteins with both peptidylprolyl isomerase (PPIase) and chaperone activities play a crucial role in protein folding in the periplasm of Gram-negative bacteria. Few such proteins have been structurally characterized and to date only the crystal structure of SurA from Escherichia coli has been reported. Par27, the prototype of a new group of parvulins, has recently been identified. Par27 exhibits both chaperone and PPIase activities in vitro and is the first identified parvulin protein that forms dimers in solution. Par27 has been expressed in E. coli. The protein was purified using affinity and gel-filtration chromatographic techniques and crystallized in two different crystal forms. Form A, which belongs to space group P2 (unit-cell parameters a = 42.2, b = 142.8, c = 56.0 A, beta = 95.1 degrees ), diffracts to 2.8 A resolution, while form B, which belongs to space group C222 (unit-cell parameters a = 54.6, b = 214.1, c = 57.8 A), diffracts to 2.2 A resolution. Preliminary diffraction data analysis agreed with the presence of one monomer in the asymmetric unit of the orthorhombic crystal form and two in the monoclinic form.

In living systems, the intramolecular cyclization of N-terminal glutamine residues is accomplished by glutaminyl cyclase enzymes (EC 2.3.2.5). While in mammals these enzymes are involved in the synthesis of hormonal and neurotransmitter peptides, the physiological role played by the corresponding plant enzymes still remains to be unravelled. Papaya glutaminyl cyclase (PQC), a 33 kDa enzyme found in the latex of the tropical tree Carica papaya, displays an exceptional resistance to chemical and thermal denaturation as well as to proteolysis. In order to elucidate its enzymatic mechanism and to gain insights into the structural determinants underlying its remarkable stability, PQC was isolated from papaya latex, purified and crystallized by the hanging-drop vapour-diffusion method. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 62.82, b = 81.23, c = 108.17 A and two molecules per asymmetric unit. Diffraction data have been collected at ESRF beamline BM14 and processed to a resolution of 1.7 A.