Intramolecular amide bonds stabilize pili on the surface of bacilli

Abstract

Gram-positive bacteria elaborate pili and do so without the participation of folding chaperones or disulfide bond catalysts. Sortases, enzymes that cut pilin precursors, form covalent bonds that link pilin subunits and assemble pili on the bacterial surface. We determined the x-ray structure of BcpA, the major pilin subunit of Bacillus cereus . The BcpA precursor encompasses 2 Ig folds (CNA 2 and CNA 3 ) and one jelly-roll domain (XNA) each of which synthesizes a single intramolecular amide bond. A fourth amide bond, derived from the Ig fold of CNA 1 , is formed only after pilin subunits have been incorporated into pili. We report that the domains of pilin precursors have evolved to synthesize a discrete sequence of intramolecular amide bonds, thereby conferring structural stability and protease resistance to pili.

Structure-based approach to rationally design a chimeric protein for an effective vaccine against Group B Streptococcus infections

“…Furthermore, they carry intramolecular isopeptide bonds, which represent the Gram-positive counterparts of disulfide bonds found in Gram-negative bacterial pili. Isopeptide bonds are the result of an autocatalytic reaction that renders pili extremely resistant to proteolysis and high temperatures (19,20).…”

The Two Variants of the Streptococcus pneumoniae Pilus 1 RrgA Adhesin Retain the Same Function and Elicit Cross-Protection In Vivo

“…These structures are composed of subunits covalently linked by means of intermolecular isopeptide bonds (32,36,(51)(52)(53). Furthermore, intramolecular isopeptide bonds have been found in most pilus subunits characterized to date (9,(26)(27)(28). These bonds may play a critical role in maintaining pilus integrity in the face of severe mechanical and chemical stress while bound to host cells and thus may provide a functional mode of stabilization for cell surface proteins involved in host pathogenesis.…”

Structural biology of gram‐positive bacterial adhesins

“…18,39,40 The pilin motif Lys residue is involved in the intermolecular isopeptide bond, and the neighboring Asn residue participates in the N1 domain intramolecular/domain isopeptide bond. In a significant discovery, revealed that during the pilus polymerization, the intramolecular isopeptide bond in the N1 domain forms only after the major pilin precursor participates in Lys-Thr inter-molecular amide bond formation, 41 leading to a polymerized and stable pilus shaft.…”

“…4(d)]. 18 Each domain contains an isopeptide bond, including the N1 domain, in which the isopeptide bond is shown to be formed during the pilus polymerization. The N2 and N4 domains have E-type isopeptide bonds, in trans and cis configurations, respectively, and the N3 domain has a D-type isopeptide bond in a cis configuration.…”

“…This inter-molecular cross-linking catalyzed by a specific sortase, as demonstrated for Corynebacterium diphtheriae pilus assembly, 7,8 is unique to Gram-positives. To date, crystal structures are available for many full-length or fragments of individual pilins (Table I), [15][16][17][18] but, unlike the surface proteins, the type of ligands they target and their binding mode are still unclear. One important common building block for both types of Gram-positive adhesins is the IgG-constant domain, which appears in two or more different forms that are different from the widely observed V-, C-, H-, and I-type folds of the immunoglobulin superfamily.…”