Expression, purification, crystallization and preliminary diffraction analysis of CapF, a capsular polysaccharide-synthesis enzyme from Staphylococcus aureus.

Capsular polysaccharides (CPs) are important virulence factors of Staphylococcus aureus. The biosynthesis of type 5 and type 8 CPs (CP5 and CP8), which are produced by most clinical isolates of S. aureus, is catalyzed by 16 CP-assembling proteins. One of these proteins is the enzyme CapF, which catalyzes the synthesis of UDP-N-acetyl-L-fucosamine, a component of both CP5 and CP8. Here, the cloning, expression, purification, crystallization and diffraction analysis of CapF are reported. Optimization of the crystallization conditions by differential scanning calorimetry afforded a crystal of selenomethionine-substituted CapF that diffracted to a resolution of 2.80 A. The crystal belongs to space group P3(2)21, with unit-cell parameters a = b = 119.6, c = 129.5 A.