Pilin: Difference between revisions

The cysteine-containing region in the C-terminus is thought to play a function via the formation of disulfides in CFTR adhesion and in the assembly of PilS to make the pilus of the bacterium. The highly conserved N-terminal hydrophobic tail functions as a oligomerization domain for fibre formation. <ref name=journal2>Asha M. Balakrishna,Yvonne Yih-Wan Tan, Henry Yu-Keung Mok,Anand M. Saxena,and Kunchithapadam Swaminathan. Crystallization and preliminary X-ray diffraction analysis of Salmonella typhi PilS. 2006 October 1; 62(Pt 10): 1024–1026</ref> The D-region of the type IVb pilins is known to contain residues that function in pilus assembly; this region is stabilized by a conserved disulfide bond. <ref name=journal1>PMID:19626704</ref>

                 [[Image:N_Teeerminal_Hydrophobic.png|thumb|Highly Conserved N-Terminal Helix of the Type IVb Pilin]]

192 water molecules and 2107 non-hydrogen atoms are found in the native structure of PilS and the loop regions of this protein are highly flexible. The crystal structure of PilS contains the standard αβ fold of the type IVb pilin, with a central anti-parallel β-sheet platform that is made up of seven β strands, and surrounded by four α helices. The complete β sheet topology of PilS is β1-β2-β3-β4-β7-β5-β6. <ref name=journal1>PMID:19626704</ref> The N-terminal alpha helix (α1) can be found on three of these strands (β3, β4, and β7).The alpha helix of the type IVb pilins is straight, as there is no proline or glycine present in positions that would disturb the structure of the helix. The region between the N-terminal alpha helix and β3 (the αβ-loop) contains another alpha helix (α2) and also a pair of anti-parallel β-strands (β1 and β2). Helix α2 packs almost perpendicular to and on top of helix α1, causing helix α2, strand β1, and the α1-α2 loop of PilS to be all located on one side of the molecule. Finally, a disulfide bridge links the residues Cys126 and Cys 163. <ref name=journal1>PMID:19626704</ref>