Structural basis for Myf and Psa fimbriae‐mediated tropism of pathogenic strains of Yersinia for host tissues

Abstract

Three pathogenic species of the genus Yersinia assemble adhesive fimbriae via the FGL-chaperone/usher pathway. Closely related Y. pestis and Y. pseudotuberculosis elaborate the pH6 antigen (Psa), which mediates bacterial attachment to alveolar cells of the lung. Y. enterocolitica, instead, assembles the homologous fimbriae Myf of unknown function. Here, we discovered that Myf, like Psa, specifically recognizes β1-3- or β1-4-linked galactose in glycosphingolipids, but completely lacks affinity for phosphatidylcholine, the main receptor for Psa in alveolar cells. The crystal structure of a subunit of Psa (PsaA) complexed with choline together with mutagenesis experiments revealed that PsaA has four phosphatidylcholine binding pockets that enable super-high-avidity binding of Psa-fibres to cell membranes. The pockets are arranged as six tyrosine residues, which are all missing in the MyfA subunit of Myf. Conversely, the crystal structure of the MyfA-galactose complex revealed that the galactose-binding site is more extended in MyfA, enabling tighter binding to lactosyl moieties. Our results suggest that during evolution, Psa has acquired a tyrosine-rich surface that enables it to bind to phosphatidylcholine and mediate adhesion of Y. pestis/pseudotuberculosis to alveolar cells, whereas Myf has specialized as a carbohydrate-binding adhesin, facilitating the attachment of Y. enterocolitica to intestinal cells.

Structural basis for Acinetobacter baumannii biofilm formation

“…5 ). Like many other proteins, which function relies on substrate or receptor recognition, classical pili use a depression or a binding cavity, which is complementary in shape and chemical properties to the minimal binding determinant of the host cell receptor ( 13 – 15 , 25 , 26 ). Our study shows that archaic pili have no such binding cavity.…”

“…Oligonucleotides are listed in SI Appendix , Table S2 . Expression plasmids were constructed based on the pBAD-ENSPA plasmid ( 25 ) or pET101D expression vector (Invitrogen) as described in SI Appendix . The pBAD-Csu plasmid and its derivatives were used to express wild-type and mutant Csu pili, and the pET101-CsuENPD6H plasmid and its derivative were used to express wild-type and mutant CsuE NTD .…”

Structural and functional dissection reveals distinct roles of Ca2+-binding sites in the giant adhesin SiiE of Salmonella enterica

“…74 W, in most of the BIg domains. This residue is distal to the Ca 2+ -binding sites, but may be involved in interaction of SiiE with glycostructures as observed for transport proteins [15] or fimbrial adhesins [16]. …”

Methylation, crystallization and SAD phasing of the Csu pilus CsuC–CsuE chaperone–adhesin subunit pre-assembly complex from Acinetobacter baumannii

“…Structural flexibility could be reduced by the methylation of lysine residues (Walter et al, 2006). In addition, methylation increases hydrophobicity, which could also be beneficial as CsuC-CsuE, like other proteins from the CU pathway (Berry et al, 2014;Roy et al, 2012;Pakharukova et al, 2016), is highly soluble, requiring large amounts of protein for crystallization experiments. Reductive methylation of lysine residues in CsuC-CsuE led to a significant loss of the complex (nearly 50%) owing to precipitation.…”