MS11-P10 Structural studies of the five pilin proteins building up the type-V pilus Mfa1 of Porphyromonas gingivalisStructural and functional information of pili from the Bacteroidetes class of bacteria is sparse. Porphyromonas gingivalis, a periodontal pathogen belonging to the Bacteroidetes class, expresses two forms of pili, FimA and Mfa1. Each pilus consists of five proteins; FimA-E and Mfa1-5 respectively. Both represent the type-V form of pili. While the structure and assembly of type-1 pili from Escherichia coli is well studied, the chaperone-usher pathway, very little is known about the polymerization of type-V pili. In order to obtain an understanding of the structure, function and assembly mechanism of the P. gingivalis pili we have solved the X-ray crystal structures of all five Mfa proteins in recombinant form [1,2]. Despite low sequence similarity the Mfa1-4 proteins are structurally related to each other being built up from two β-sandwich domains. The P. gingivalis pilin proteins start as lipidated precursors before they are transported to the surface and polymerized. The precursor comprises an N-terminal extension, which is cleaved off upon polymerization. Intriguingly, all proteins were crystallized in their precursor forms with their N-terminal extensions still present. Part of this extension forms the first strand of the first β-sheet of the pilin. Maturation of the pilin is the result of cleaving the polypeptide at a conserved arginine downstream of this first β-strand resulting in a new N-terminus and a void in the first β-sheet. In analogy with the strand-displacement mechanism used for polymerization of the type-1 pili we believe that the void is filled by a donor β-strand from another pilin protein. However, despite having the crystal structure of all Mfa1-4 proteins and data from several mutagenesis studies we still do not know if it is the newly formed N-terminus or the long flexible C-terminus present on Mfa1 that constitute the donor strand.
The final protein, Mfa5, differs from the other Mfa proteins; it is much larger and consists of an N-terminal von Willebrand domain followed by a string of Ig-like domains .
1. Kloppsteck, P. et al. (2016). Scientific reports 6, 22945
2. Hall, M. et al. (2018). Scientific reports 8, 1793
3. Hasegawa, Y. et al. (2016) J Dent Res 95, 1291-1297
Keywords: pili, polymerization, bacteria