Crystal structure of lactobacillar SpaC reveals an atypical five-domain pilus tip adhesin: Exposing its substrate-binding and assembly in SpaCBA pili

Abhiruchi Kant, Airi Palva, Ingemar von Ossowski, Vengadesan Krishnan*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Adhesion to cell surfaces is an essential and early prerequisite for successful host colonization by bacteria, and in most instances involves the specificities of various adhesins. Among bacterial Gram-positives, some genera and species mediate attachment to host cells by using long non-flagellar appendages called sortase-dependent pili. A case in point is the beneficial Lactobacillus rhamnosus GG gut-adapted strain that produces the so-called SpaCBA pilus, a structure noted for its promiscuous binding to intestinal mucus and collagen. Structurally, SpaCBA pili are heteropolymers of three different pilin-protein subunits, each with its own location and function in the pilus: backbone SpaA for length, basal SpaB for anchoring, and tip SpaC for adhesion. Previously, we solved the SpaA tertiary structure by X-ray crystallography and also reported on the crystallization of SpaB and SpaC. Here, we reveal the full-length high-resolution (1.9 angstrom) crystal structure of SpaC, a first for a sortase-dependent pilus-bearing commensal. The SpaC structure, unlike the representative four-domain architecture of other Grampositive tip pilins, espouses an atypically longer five-domain arrangement that includes N-terminal 'binding' and C-terminal 'stalk' regions of two and three domains, respectively. With the prospect of establishing new mechanistic insights, we provide a structural basis for the multi-substrate binding nature of SpaC, as well as a structural model that reconciles its exclusive localization at the SpaCBA pilus tip.

Original languageEnglish
Article number107571
Number of pages16
JournalJournal of Structural Biology
Volume211
Issue number3
DOIs
Publication statusPublished - 1 Sep 2020
MoE publication typeA1 Journal article-refereed

Keywords

  • Sortase-dependent pili
  • Tip pilin
  • Adhesion
  • Mucin
  • Collagen
  • Lactobacillus rhamnosus GG
  • Lectin
  • Probiotics
  • GRAM-POSITIVE BACTERIA
  • RAY-DIFFRACTION ANALYSIS
  • RHAMNOSUS GG PILI
  • CRYSTALLOGRAPHIC ANALYSIS
  • ISOPEPTIDE BONDS
  • A-DOMAIN
  • I-DOMAIN
  • INTEGRIN
  • COLLAGEN
  • CRYSTALLIZATION

Cite this