title: Crystal structure of the N-terminal domain of the secretin GspD from ETEC determined with the assistance of a nanobody.
abstract: Secretins are among the largest bacterial outer membrane proteins known. Here we report the crystal structure of the periplasmic N-terminal domain of GspD (peri-GspD) from the type 2 secretion system (T2SS) secretin in complex with a nanobody, the VHH domain of a heavy-chain camelid antibody. Two different crystal forms contained the same compact peri-GspD:nanobody heterotetramer. The nanobody contacts peri-GspD mainly via CDR3 and framework residues. The peri-GspD structure reveals three subdomains, with the second and third subdomains exhibiting the KH fold which also occurs in ring-forming proteins of the type 3 secretion system. The first subdomain of GspD is related to domains in phage tail proteins and outer membrane TonB-dependent receptors. A dodecameric peri-GspD model is proposed in which a solvent-accessible beta strand of the first subdomain interacts with secreted proteins and/or T2SS partner proteins by beta strand complementation.
authors.affiliation: Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, WA 98195, USA.
authors.forename: Konstantin V
authors.initials: KV
authors.lastname: Korotkov
authors.forename: Els
authors.initials: E
authors.lastname: Pardon
authors.forename: Jan
authors.initials: J
authors.lastname: Steyaert
authors.forename: Wim G J
authors.initials: WG
authors.lastname: Hol
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D054307:Enterotoxigenic Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018272:Porins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization / Q000502:physiology; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012633:Secretin / Q000737:chemistry* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D029968:Escherichia coli Proteins; C540076:GspD protein, E coli; D007143:Immunoglobulin Heavy Chains; D018272:Porins; D012633:Secretin