title: Cell-surface display of a Pseudomonas aeruginosa strain K pilin peptide within the paracrystalline S-layer of Caulobacter crescentus.
abstract: The paracrystalline surface (S)-layer of Caulobacter crescentus is composed of a single secreted protein (RsaA) that interlocks in a hexagonal pattern to completely envelop the bacterium. Using a genetic approach, we inserted a 12 amino acid peptide from Pseudomonas aeruginosa strain K pilin at numerous semirandom positions in RsaA. We then used an immunological screen to identify those sites that presented the inserted pilin peptide on the C. crescentus cell surface as a part of the S-layer. Eleven such sites (widely separated in the primary sequence) were identified, demonstrating for the first time that S-layers can be readily exploited as carrier proteins to display 'epitope-size' heterologous peptides on bacterial cell surfaces. Whereas intact RsaA molecules carrying a pilin peptide could always be found on the surface of C. crescentus regardless of the particular insertion site, introduction of the pilin peptide at 9 of the 11 sites resulted in some proteolytic cleavage of RsaA. Two types of proteolytic phenomena were observed. The first was characterized by a single cleavage within the pilin peptide insert with both fragments of the S-layer protein remaining anchored to the outer membrane. The other proteolytic phenomenon was characterized by cleavage of the S-layer protein at a point distant from the site of the pilin peptide insertion. This cleavage always occurred at the same location in RsaA regardless of the particular insertion site, yielding a surface-anchored 26 kDa proteolytic fragment bearing the RsaA N-terminus; the C-terminal cleavage product carrying the pilin peptide was released into the growth medium. When the results of this work were combined with the results of a previous study, the RsaA primary sequence could be divided into three regions with respect to the location of a peptide insertion and its effect on S-layer biogenesis: (i) insertions in the extreme N-terminus of RsaA either produce no apparent effect on S-layer biogenesis or disrupt surface-anchoring of the protein; (ii) insertions in the extreme C-terminus either produce no apparent effect on S-layer biogenesis or disrupt protein secretion; and (iii) insertions more centrally located in the protein either have no apparent effect on S-layer biogenesis or result in proteolytic cleavage of RsaA. These data are discussed in relation to our previous assignment of the RsaA N- and C-terminus as regions that are important for surface anchoring and secretion respectively.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
authors.forename: W H
authors.initials: WH
authors.lastname: Bingle
authors.forename: J F
authors.initials: JF
authors.lastname: Nomellini
authors.forename: J
authors.initials: J
authors.lastname: Smit
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism* / Q000648:ultrastructure; D001426:Bacterial Proteins; D016935:Caulobacter crescentus / Q000378:metabolism*; D036781:Fimbriae Proteins; D008562:Membrane Glycoproteins; D011550:Pseudomonas aeruginosa / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins; D036781:Fimbriae Proteins