title: Crystal structure and functional studies reveal that PAS factor from Vibrio vulnificus is a novel member of the saposin-fold family.
abstract: PAS factor is a novel putative bacterial secretion factor thought to induce secretion of periplasmic proteins. We solved the crystal structure of PAS factor from Vibrio vulnificus at 1.8A resolution and found it to be comprised of five alpha helices that form an antiparallel bundle with an up-and-down topology, and to adopt the saposin-fold characteristic of a family of proteins that bind to membranes and lipids. PAS factor lacks the disulfide bridge characteristic of mammalian saposin-fold proteins; in fact, it shows no sequence homology with mammalian proteins. Nevertheless, the molecular architectures are similar, and the shared propensity for membrane interaction suggests strongly that PAS factor is another member of the saposin-fold family. Analysis of the CD spectra showed that PAS factor binds to membranes directly, while measurement of calcein dye leakage showed that PAS factor interacts strongly with liposomes composed of anionic phospholipids, making them leaky, but binds very weakly with liposomes composed of zwitterionic phospholipids. Moreover, by analyzing tryptophan fluorescence emission from four single-tryptophan mutants (V10W, T22W, F35W, and L70W), we identified the putative phospholipid-binding site of PAS factor. The resultant membrane destabilization likely mediates secretion of periplasmic proteins required for the in vivo survival and pathogenesis of V.vulnificus.
authors.affiliation: Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: Jun Hyuck
authors.initials: JH
authors.lastname: Lee
authors.forename: Sung-Tae
authors.initials: ST
authors.lastname: Yang
authors.forename: Seong-Hwan
authors.initials: SH
authors.lastname: Rho
authors.forename: Young Jun
authors.initials: YJ
authors.lastname: Im
authors.forename: Soo Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Young Ran
authors.initials: YR
authors.lastname: Kim
authors.forename: Mun-Kyoung
authors.initials: MK
authors.lastname: Kim
authors.forename: Gil Bu
authors.initials: GB
authors.lastname: Kang
authors.forename: Jae Il
authors.initials: JI
authors.lastname: Kim
authors.forename: Joon Haeng
authors.initials: JH
authors.lastname: Rhee
authors.forename: Soo Hyun
authors.initials: SH
authors.lastname: Eom
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D005452:Fluoresceins / Q000737:chemistry; D005453:Fluorescence; D005456:Fluorescent Dyes; D008081:Liposomes / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010743:Phospholipids / Q000737:chemistry; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D049231:Saposins / Q000737:chemistry* / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014364:Tryptophan / Q000737:chemistry / Q000235:genetics; D041261:Vibrio vulnificus / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008081:Liposomes; D010743:Phospholipids; D011994:Recombinant Proteins; D049231:Saposins; D014364:Tryptophan; C007740:fluorexon