Purification, crystallization and preliminary crystallographic analysis of the minor pilin FctB from Streptococcus pyogenes

The minor pilin FctB is an integral part of the pilus assembly expressed by Streptococcus pyogenes. Since it is located at the cell wall, it can be hypothesized that it functions as a cell-wall anchor for the streptococcal pilus. In order to elucidate its structure, the genes for FctB from the S. pyogenes strains 90/306S and SF370 were cloned for overexpression in Escherichia coli. FctB from strain 90/306S was crystallized by the sitting-drop vapour-diffusion method using sodium citrate as a precipitant. The hexagonal FctB crystals belonged to space group P6₁ or P6₅, with unit-cell parameters a = b = 95.15, c = 100.25 Å, and diffracted to 2.9 Å resolution.