Figure 8.

Crystal structures of representative tip and major pilins. The RrgA tip pilin of S. pneumoniae (PDB ID: 2WW8) is shown on the left, with the fold adopted by each of the four subdomains indicated. The VWA domain is depicted in green, with the residues forming the MIDAS motif and bound magnesium ion shown in purple. The residues involved in intramolecular isopeptide bond formation are shown in red. The Spy0128 major pilin of S. pyogenes (PDB ID: 3B2M) is depicted on the right in purple and the two subdomains are labeled as for RrgA. The lysine side chain of Syp0128 thought to be involved in intermolecular isopeptide bond formation is shown in cyan.