title: Structural and population characterization of MrkD, the adhesive subunit of type 3 fimbriae.
abstract: Type 3 fimbriae are adhesive organelles found in enterobacterial pathogens. The fimbriae promote biofilm formation on biotic and abiotic surfaces; however, the exact identity of the receptor for the type 3 fimbriae adhesin, MrkD, remains elusive. We analyzed naturally occurring structural and functional variabilities of the MrkD adhesin from Klebsiella pneumoniae and Escherichia coli isolates of diverse origins. We identified a total of 33 allelic variants of mrkD among 90 K. pneumoniae isolates and 10 allelic variants among 608 E. coli isolates, encoding 11 and 9 protein variants, respectively. Based on the level of accumulated silent variability between the alleles, mrkD was acquired a relatively long time ago in K. pneumoniae but recently in E. coli. However, unlike K. pneumoniae, mrkD in E. coli is actively evolving under a strong positive selection by accumulation of mutations, often targeting the same positions in the protein. Several naturally occurring MrkD protein variants from E. coli were found to be significantly less adherent when tested in a mannan-binding assay and showed reduced biofilm-forming capacity. Functional examination of the MrkD adhesin in flow chamber experiments determined that it interacts with Saccharomyces cerevisiae cells in a shear-dependent manner, i.e., the binding is catch-bond-like and enhanced under increasing shear conditions. Homology modeling strongly suggested that MrkD has a two-domain structure, comprising a pilin domain anchoring the adhesin to the fimbrial shaft and a lectin domain containing the binding pocket; this is similar to structures found in other catch-bond-forming fimbrial adhesins in enterobacteria.
authors.affiliation: Department of Microbiology and Infection Control, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Steen G
authors.initials: SG
authors.lastname: Stahlhut
authors.forename: Sujay
authors.initials: S
authors.lastname: Chattopadhyay
authors.forename: Dagmara I
authors.initials: DI
authors.lastname: Kisiela
authors.forename: Kristian
authors.initials: K
authors.lastname: Hvidtfeldt
authors.forename: Steven
authors.initials: S
authors.lastname: Clegg
authors.forename: Carsten
authors.initials: C
authors.lastname: Struve
authors.forename: Evgeni V
authors.initials: EV
authors.lastname: Sokurenko
authors.forename: Karen A
authors.initials: KA
authors.lastname: Krogfelt
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018830:Adhesins, Escherichia coli; D000483:Alleles; D001422:Bacterial Adhesion; D018441:Biofilms / Q000254:growth & development; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D036781:Fimbriae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014644:Genetic Variation; D007711:Klebsiella pneumoniae / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D056265:Microbial Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000502:physiology; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA
chemical_list: D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C058768:Klebsiella pneumoniae type 3 fimbrial adhesin; C585835:MrkD protein, E coli; D036781:Fimbriae Proteins