Crystallization of the factor H-binding protein, FhbB, from the periopathogen Treponema denticola

Treponema denticola is a primary etiological agent of periodontal disease. T. denticola evades complement-mediated killing by binding to the host's factor H (FH), a negative regulator of the alternative complement pathway. The T. denticola FH-binding protein has been identified and designated as factor H-binding protein B (FhbB). Crystals of recombinant FhbB were obtained by the hanging-drop vapor-diffusion method using sodium citrate and 0.2 M sodium thiocyanate. FhbB crystals diffracted to 1.8 Å resolution and belonged to space group P4(3)2(1)2 or P4(1)2(1)2, with unit-cell parameters a = b = 46.76, c = 167.68 Å. Two FhbB molecules per asymmetric unit gave a Matthews coefficient of 2.2 Å(3) Da(-1) and a solvent content of 44%. FhbB is the smallest bacterially produced FH-binding protein identified to date. Determination of its structure will provide unique insight into the minimal structural determinants required for FH binding.