Crystallization and X-ray crystallographic analysis of the adhesive SpaC pilin subunit in the SpaCBA pilus of gut-adapted Lactobacillus rhamnosus GG

Gram-positive lactobacillus rhamnosus gg,a gut-adapted commensalic (and probiotic) strain,is known to express sortase-assembled pili on its cell surface. these spacba-called pili consist of three different types of building blocks; the spaa backbone-pilin subunit and the spab and spac ancillary pilins. spac is a relatively large (∼90kda) multi-domain fimbrial adhesin,and while it is located primarily at the spacba pilus tip,occasionally,it can also be detected throughout the length of pilus backbone. functionally,spac mainly accounts for spacba pilus-mediated interactions with intestinal mucus,collagen,and human gut epithelial cells. moreover,spac adhesiveness is also perceived to have a causal relationship with spacba pilus-induced host-cell immune responses. in order to improve the mechanistic understanding of spac and its adhesive properties by structural investigation,we purified and successfully crystallized a recombinant construct of the near full-length spac protein (residues 36-856) in the presence of magnesium ions. x-ray diffraction data were collected to 2.6 å resolution. the spac crystal belongs to the space group p21212 with unit cell parameters a = 116.5,b = 128.3,c = 136.5 å and contains two molecules in the asymmetric unit. presence of conserved metal ion-dependent adhesion site containing von willebrand factor type a domain suggests its likely role in the function of spac. © 2016 bentham science publishers.