title: Unique secreted-surface protein complex of Lactobacillus rhamnosus, identified by phage display.
abstract: Proteins are the most diverse structures on bacterial surfaces; hence, they are candidates for species- and strain-specific interactions of bacteria with the host, environment, and other microorganisms. Genomics has decoded thousands of bacterial surface and secreted proteins, yet the function of most cannot be predicted because of the enormous variability and a lack of experimental data that would allow deduction of function through homology. Here, we used phage display to identify a pair of interacting extracellular proteins in the probiotic bacterium Lactobacillus rhamnosus HN001. A secreted protein, SpcA, containing two bacterial immunoglobulin-like domains type 3 (Big-3) and a domain distantly related to plant pathogen response domain 1 (PR-1-like) was identified by screening of an L. rhamnosus HN001 library using HN001 cells as bait. The SpcA-"docking" protein, SpcB, was in turn detected by another phage display library screening, using purified SpcA as bait. SpcB is a 3275-residue cell-surface protein that contains general features of large glycosylated Serine-rich adhesins/fibrils from gram-positive bacteria, including the hallmark signal sequence motif KxYKxGKxW. Both proteins are encoded by genes within a L. rhamnosus-unique gene cluster that distinguishes this species from other lactobacilli. To our knowledge, this is the first example of a secreted-docking protein pair identified in lactobacilli.
authors.affiliation: Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
authors.forename: Dragana
authors.initials: D
authors.lastname: Gagic
authors.forename: Wesley
authors.initials: W
authors.lastname: Wen
authors.forename: Michael A
authors.initials: MA
authors.lastname: Collett
authors.forename: Jasna
authors.initials: J
authors.lastname: Rakonjac
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D061505:Cell Surface Display Techniques; D015723:Gene Library; D052201:Lacticaseibacillus rhamnosus / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping
chemical_list: D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D008565:Membrane Proteins