title: Comparison of S-layer secretion genes in freshwater caulobacters.
abstract: Our freshwater caulobacter collection contains about 40 strains that are morphologically similar to Caulobacter crescentus. All elaborate a crystalline protein surface (S) layer made up of protein monomers 100-193 kDa in size. We conducted a comparative study of S-layer secretion in 6 strains representing 3 size groups of S-layer proteins: small (100-108 kDa), medium (122-151 kDa), and large (181-193 kDa). All contained genes predicted to encode ATP-binding cassette transporters and membrane fusion proteins highly similar to those of C. crescentus, indicating that the S-layer proteins were all secreted by a type I system. The S-layer proteins' C-termini showed unexpectedly low sequence similarity but contained conserved residues and predicted secondary structure features typical of type I secretion signals. Cross-expression studies showed that the 6 strains recognized secretion signals from C. crescentus and Pseudomonas aeruginosa and similarly that C. crescentus was able to secrete the S-layer protein C-terminus of 1 strain examined. Inactivation of the ATP-binding cassette transporter abolished S-layer protein secretion, indicating that the type I transporter is necessary for S-layer protein secretion. Finally, while all of the S-layer proteins of this subset of strains were secreted by type I mechanisms, there were significant differences in genome positions of the transporter genes that correlated with S-layer protein size.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
authors.forename: Mihai
authors.initials: M
authors.lastname: Iuga
authors.forename: Peter
authors.initials: P
authors.lastname: Awram
authors.forename: John F
authors.initials: JF
authors.lastname: Nomellini
authors.forename: John
authors.initials: J
authors.lastname: Smit
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016934:Caulobacter / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016935:Caulobacter crescentus / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D005618:Fresh Water / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins