title: Assembly mechanism of FCT region type 1 pili in serotype M6 Streptococcus pyogenes.
abstract: The human pathogen Streptococcus pyogenes produces diverse pili depending on the serotype. We investigated the assembly mechanism of FCT type 1 pili in a serotype M6 strain. The pili were found to be assembled from two precursor proteins, the backbone protein T6 and ancillary protein FctX, and anchored to the cell wall in a manner that requires both a housekeeping sortase enzyme (SrtA) and pilus-associated sortase enzyme (SrtB). SrtB is primarily required for efficient formation of the T6 and FctX complex and subsequent polymerization of T6, whereas proper anchoring of the pili to the cell wall is mainly mediated by SrtA. Because motifs essential for polymerization of pilus backbone proteins in other Gram-positive bacteria are not present in T6, we sought to identify the functional residues involved in this process. Our results showed that T6 encompasses the novel VAKS pilin motif conserved in streptococcal T6 homologues and that the lysine residue (Lys-175) within the motif and cell wall sorting signal of T6 are prerequisites for isopeptide linkage of T6 molecules. Because Lys-175 and the cell wall sorting signal of FctX are indispensable for substantial incorporation of FctX into the T6 pilus shaft, FctX is suggested to be located at the pilus tip, which was also implied by immunogold electron microscopy findings. Thus, the elaborate assembly of FCT type 1 pili is potentially organized by sortase-mediated cross-linking between sorting signals and the amino group of Lys-175 positioned in the VAKS motif of T6, thereby displaying T6 and FctX in a temporospatial manner.
authors: Department of Oral and Molecular Microbiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita-Osaka, 565-0871, Japan.
authors: Masanobu
authors: M
authors: Nakata
authors: Keiji Richard
authors: KR
authors: Kimura
authors: Tomoko
authors: T
authors: Sumitomo
authors: Satoshi
authors: S
authors: Wada
authors: Akinari
authors: A
authors: Sugauchi
authors: Eiji
authors: E
authors: Oiki
authors: Miharu
authors: M
authors: Higashino
authors: Bernd
authors: B
authors: Kreikemeyer
authors: Andreas
authors: A
authors: Podbielski
authors: Nobuo
authors: N
authors: Okahashi
authors: Shigeyuki
authors: S
authors: Hamada
authors: Ryutaro
authors: R
authors: Isoda
authors: Yutaka
authors: Y
authors: Terao
authors: Shigetada
authors: S
authors: Kawabata
mesh_terms: D020816:Amino Acid Motifs; D001483:Base Sequence; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D008969:Molecular Sequence Data; D055503:Protein Multimerization / Q000502:physiology*; D013297:Streptococcus pyogenes / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D036781:Fimbriae Proteins