Structural and antigenic characterization of a novel genotype of Mfa1 fimbriae in Porphyromonas gingivalis

BACKGROUND: Mfa1 fimbriae of the periodontal pathogen Porphyromonas gingivalis are responsible for biofilm formation and comprise five proteins: Mfa1–5. Two major genotypes, mfa1(70) and mfa1(53), encode major fimbrillin. The mfa1(70) genotype is further divided into the mfa1(70A) and mfa1(70B) subtypes. The properties of the novel mfa1(70B) remain unclear. METHODS: Fimbriae were purified from P. gingivalis strains JI-1 (mfa1(70A)), 1439 (mfa1(70B)), and Ando (mfa1(53)), and their components and their structures were analyzed. Protein expression and variability in the antigenic specificity of fimbrillins were compared using Coomassie staining and western blotting using polyclonal antibodies against Mfa1(70A), Mfa1(70B), and Mfa1(53) proteins. Cell surface expression levels of fimbriae were analyzed by filtration enzyme-linked immunosorbent assays. RESULTS: The composition and structures of the purified Mfa1 fimbriae of 1439 was similar to that of JI-1. However, each Mfa1 protein of differential subtype/genotype was specifically detected by western blotting. Mfa1(70B) fimbriae were expressed in several strains such as 1439, JKG9, B42, 1436, and Kyudai-3. Differential protein expression and antigenic heterogeneities were detected in Mfa2–5 between strains. CONCLUSION: Mfa1 fimbriae from the mfa170A and mfa170B genotypes indicated an antigenic difference suggesting the mfa170B, is to be utilized for the novel classification of P. gingivalis.