PDBsum entry 5hdl

Cell adhesion

PDB id: 5hdl

Contents

Protein chains

265 a.a.

Waters ×171

References listed in PDB file

Key reference

• Title: New insights about pilus formation in gut-Adapted lactobacillus rhamnosus gg from the crystal structure of the spaa backbone-Pilin subunit.
• Authors: P.Chaurasia, S.Pratap, I.Von ossowski, A.Palva, V.Krishnan.
• Ref.: Sci Rep, 2016, 6, 28664. [DOI no: 10.1038/srep28664]
• PubMed id: 27349405

Abstract

Thus far, all solved structures of pilin-proteins comprising sortase-assembled pili are from pathogenic genera and species. Here, we present the first crystal structure of a pilin subunit (SpaA) from a non-pathogen host (Lactobacillus rhamnosus GG). SpaA consists of two tandem CnaB-type domains, each with an isopeptide bond and E-box motif. Intriguingly, while the isopeptide bond in the N-terminal domain forms between lysine and asparagine, the one in the C-terminal domain atypically involves aspartate. We also solved crystal structures of mutant proteins where residues implicated in forming isopeptide bonds were replaced. Expectedly, the E-box-substituted E139A mutant lacks an isopeptide bond in the N-terminal domain. However, the C-terminal E269A substitution gave two structures; one of both domains with their isopeptide bonds present, and another of only the N-terminal domain, but with an unformed isopeptide bond and significant conformational changes. This latter crystal structure has never been observed for any other Gram-positive pilin. Notably, the C-terminal isopeptide bond still forms in D295N-substituted SpaA, irrespective of E269 being present or absent. Although E-box mutations affect SpaA proteolytic and thermal stability, a cumulative effect perturbing normal pilus polymerization was unobserved. A model showing the polymerized arrangement of SpaA within the SpaCBA pilus is proposed.