Crystallization and preliminary crystallographic analysis of the type III secretion translocator chaperone SicA from Salmonella enterica.

SicA is a member of the class II chaperones in type III secretion systems which bind to the pore-forming translocators in the bacterial cytoplasm and prevent them from premature association and degradation. In this study, SicA from Salmonella enterica serovar Typhimurium was overexpressed, purified and crystallized using PEG 8000 as the precipitant. X-ray diffraction data were collected using synchrotron radiation and processed at 3.5 Å resolution. The crystal belonged to the monoclinic space group C2, with unit-cell parameters a = 180.4, b = 94.1, c = 131.8 Å, β = 130.9°. There may be eight monomers in the crystallographic asymmetric unit, corresponding to a V(M) of 2.52 Å(3) Da(-1) and a solvent content of 51.1%. This suggests an oligomerization state that differs from those of previously reported type III secretion chaperones.