title: The turn of the screw: variations of the abundant beta-solenoid motif in passenger domains of Type V secretory proteins.
abstract: Many virulence factors of gram-negative bacteria are secreted by the Type V secretion system via the autotransporter (AT) and two-partner secretion (TPS) pathways. AT proteins effect their own secretion. They comprise three domains: the amino-terminal leader sequence; the secreted passenger domain; and the translocator domain that forms the secretory channel. In the TPS pathway, the passenger and translocator domains are translated as separate proteins. In a previous publication, we proposed a beta-helical structure for the TPS passenger domain of the filamentous hemagglutinin (FHA) of Bordetella pertussis which contains two tracts, R1 and R2, of 19-residue sequence repeats and built molecular models for the R1 and R2 beta-helices. Here, we compare the structure predicted for R1 with the recently determined crystal structure of a fragment containing three R1 repeats and find close agreement, with an RMSD of 1.1A. In the interim, the number of known AT and TPS protein sequences has increased to >1000. To investigate the incidence of beta-helical structures among them, we carried out a sequence-based analysis and conclude that, despite wide diversity in the sizes and sequences of passenger domains, most of them contain beta-solenoids that we classify into thirteen types based on distinctive properties of their beta-coils (repeat length, numbers and lengths of beta-strands and turns, cross-sectional shape, presence of specific residues in certain positions) summarized in a 2D coil template. Some coil types are typical for conventional AT proteins, others, for TPS or trimeric AT proteins. Some beta-solenoids consist of stacked subdomains with coils of different types. To illustrate model-building from a coil template, we modeled a type-T4 beta-solenoid for TibA of Escherichia coli which is predicted to have two conserved polar residues, Thr and Gln, in interior positions.
authors.affiliation: Centre de Recherches de Biochimie Macromoléculaire, CNRS FRE-2593, 1919 Route de Mende, 34293 Montpellier, Cedex 5, France. Andrey.Kajava@crbm.cnrs.fr
authors.forename: Andrey V
authors.initials: AV
authors.lastname: Kajava
authors.forename: Alasdair C
authors.initials: AC
authors.lastname: Steven
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D019295:Computational Biology / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D010566:Virulence Factors, Bordetella / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D018829:Adhesins, Bacterial; D010566:Virulence Factors, Bordetella; C065273:filamentous hemagglutinin adhesin, Bordetella pertussis