Crystallization and preliminary X-ray analysis of the periplasmic domain of FliP, an integral membrane component of the bacterial flagellar type III protein-export apparatus

Abstract

The bacterial flagellar proteins are transportedviaa specific export apparatus to the distal end of the growing structure for their self-assembly. FliP is an essential membrane component of the export apparatus. FliP has an N-terminal signal peptide and is predicted to have four transmembrane (TM) helices and a periplasmic domain (FliPP) between TM-2 and TM-3. In this study, FliPPfromThermotoga maritima(TmFliPP) and its selenomethionine derivative (SeMet-TmFliPP) were purified and crystallized. TmFliPPformed a homotetramer in solution. Crystals of TmFliPPand SeMet-TmFliPPwere obtained by the hanging-drop vapour-diffusion technique with 2-methyl-2,4-pentanediol as a precipitant. These two crystals grew in the hexagonal space groupP6222 orP6422, with unit-cell parametersa=b= 114.9,c= 193.8 Å. X-ray diffraction data were collected from crystals of TmFliPPand SeMet-TmFliPPto 2.4 and 2.8 Å resolution, respectively.