title: Isopeptide bonds in bacterial pili and their characterization by X-ray crystallography and mass spectrometry.
abstract: Pili are long, filamentous protein assemblies which extend from the surfaces of many bacteria, and mediate their adhesion to host cells and other matrices. For pathogenic bacteria they are critical to colonization and infection. Whereas the pili of gram-negative bacteria are formed by noncovalent association of their pilin subunits, those of gram-positive bacteria are assembled with the aid of sortase enzymes that mediate the formation of covalent isopeptide bonds between successive pilin subunits. Sequence comparisons, mutagenesis and crystallography have implicated specific lysine residues in the formation of these intermolecular bonds and mass spectral analyses of native and modified pili have now provided definitive proof of these linkages. Crystallographic studies of pilin subunits have also led to the unexpected discovery of internal isopeptide crosslinks formed between lysine and asparagine residues. These, too, have been confirmed by mass spectrometry.
authors.affiliation: Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland, New Zealand.
authors.forename: Hae Joo
authors.initials: HJ
authors.lastname: Kang
authors.forename: Martin
authors.initials: M
authors.lastname: Middleditch
authors.forename: Thomas
authors.initials: T
authors.lastname: Proft
authors.forename: Edward N
authors.initials: EN
authors.lastname: Baker
mesh_terms: D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D001216:Asparagine / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray; D036781:Fimbriae Proteins / Q000737:chemistry*; D010861:Fimbriae, Bacterial / Q000737:chemistry*; D006090:Gram-Negative Bacteria / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000378:metabolism; D008239:Lysine / Q000737:chemistry; D013058:Mass Spectrometry; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D010455:Peptides; D036781:Fimbriae Proteins; D001216:Asparagine; D008239:Lysine; D000409:Alanine