title: The translocation domain in trimeric autotransporter adhesins is necessary and sufficient for trimerization and autotransportation.
abstract: Trimeric autotransporter adhesins (TAAs) comprise one of the secretion pathways of the type V secretion system. The mechanism of their translocation across the outer membrane remains unclear, but it most probably occurs by the formation of a hairpin inside the β-barrel translocation unit, leading to transportation of the passenger domain from the C terminus to the N terminus through the lumen of the β-barrel. We further investigated the phenomenon of autotransportation and the rules that govern it. We showed by coexpressing different Escherichia coli immunoglobulin-binding (Eib) proteins that highly similar TAAs could form stochastically mixed structures (heterotrimers). We further investigated this phenomenon by coexpressing two more distantly related TAAs, EibA and YadA. These, however, did not form heterotrimers; indeed, coexpression was lethal to the cells, leading to elimination of one or another of the genes. However, substituting in either protein the barrel of the other one so that the barrels were identical led to formation of heterotrimers as for Eibs. Our work shows that trimerization of the β-barrel, but not the passenger domain, is necessary and sufficient for TAA secretion while the passenger domain is not.
authors.affiliation: Molecular X-Ray Crystallography Group, Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Kornelia M
authors.initials: KM
authors.lastname: Mikula
authors.forename: Jack C
authors.initials: JC
authors.lastname: Leo
authors.forename: Andrzej
authors.initials: A
authors.lastname: Łyskowski
authors.forename: Sylwia
authors.initials: S
authors.lastname: Kedracka-Krok
authors.forename: Artur
authors.initials: A
authors.lastname: Pirog
authors.forename: Adrian
authors.initials: A
authors.lastname: Goldman
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism*; D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems / Q000235:genetics / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D021381:Protein Transport
chemical_list: D018829:Adhesins, Bacterial; D001425:Bacterial Outer Membrane Proteins; D058947:Bacterial Secretion Systems; C440641:EibA protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins