FIG. 5.
Conserved lysine (K) residue in the pilin motif of SpaD is required for pilus formation. The primary structure of SpaDP precursor with an N-terminal signal peptide, C-terminal sorting signal, and cleavage sites for signal peptidase and sortase is shown. The precursors of C. diphtheriae SpaA, SpaD, and SpaH harbor a pilin motif (WxxxVxVYPK) with a conserved lysine (K) residue. Similar pilin motifs are found in FimA and FimP of A. naeslundii and C. efficiens CE2457 and CE2737 (A). Corynebacterial strains were treated with muramidase (M) or formic acid (F) or left untreated (−) prior to extraction with hot SDS sample buffer. Proteins were separated on SDS-PAGE and detected by immunoblotting with specific antiserum [α-SpaD (B), α-SpaE (C), and α-SpaF (D)]. Replacement of K107 with alanine (A) abrogates SpaDEF pilin polymerization. wt, wild type.