Structure of the fibre-forming protein pilin at 2.6 Å resolution

The crystallographic structure of Neisseria gonorrhoeae pilin, which assembles into the multi-functional pilus adhesion and virulence factor, reveals an α–β roll fold with a striking 85 Å α-helical spine and an 0-linked disaccharide. Key residues stabilize interactions that allow sequence hypervariability, responsible for pilin's celebrated antigenic variation, within disulphide region β-strands and connections. Pilin surface shape, hydrophobicity and sequence variation constrain pilus assembly to the packing of flat subunit faces against α 1 helices. Helical fibre assembly is postulated to form a core of coiled α 1 helices banded by β-sheet, leaving carbohydrate and hypervariable sequence regions exposed to solvent.