Amino acid sequence similarity among C Amino acid sequence similarity among C. difficile putative type IV pilins. Amino acid sequence similarity among C. difficile putative type IV pilins. (A) Amino acid sequences of the signal peptides and N-terminal 30 residues of the mature pilins from C. difficile strain 630. The pilins are listed as they appear in the operons in Fig. 3B. The red background indicates amino acid sequence identity; the yellow background and bold letters indicate sequence similarity (nonbolded amino acids within yellow columns are not conserved). Residues are numbered above the sequences: negative numbers are used for the signal peptide, and positive numbers are used for the mature pilin sequence. (B) Schematic comparison of C. difficile strain 13 pilins and putative pilins. Asterisks indicate putative minor pilins, among which 3506 is a GspK family member based on its large size and a leucine at position 5. The identities of the first and fifth amino acids of the mature protein are indicated, as are characteristic motifs described in the text. Gray bars represent the signal peptide, and yellow bars indicate amino acid sequence homology among the pilins within this strain. Stephen Melville, and Lisa Craig Microbiol. Mol. Biol. Rev. 2013; doi:10.1128/MMBR.00063-12