Abstract
The periodontal pathogen Porphyromonas gingivalis colonizes largely through FimA fimbriae, composed of polymerized FimA encoded by fimA. fimA exists as a single copy within the fim gene cluster (fim cluster), which consists of seven genes: fimX, pgmA and fimA-E. Using an expression vector, fimA alone was inserted into a mutant from which the whole fim cluster was deleted, and the resultant complement exhibited a fimbrial structure. Thus, the genes of the fim cluster other than fimA were not essential for the assembly of FimA fimbriae, although they were reported to influence FimA protein expression. It is known that there are various genotypes for fimA, and it was indicated that the genotype was related to the morphological features of FimA fimbriae, especially the length, and to the pathogenicity of the bacterium. We next complemented the fim cluster-deletion mutant with fimA genes cloned from P. gingivalis strains including genotypes I to V. All genotypes showed a long fimbrial structure, indicating that FimA itself had nothing to do with regulation of the fimbrial length. In FimA fimbriae purified from the complemented strains, types I, II, and III showed slightly higher thermostability than types IV and V. Antisera of mice immunized with each purified fimbria principally recognized the polymeric, structural conformation of the fimbriae, and showed low cross-reactivity among genotypes, indicating that FimA fimbriae of each genotype were antigenically different. Additionally, the activity of a macrophage cell line stimulated with the purified fimbriae was much lower than that induced by Escherichia coli lipopolysaccharide.
Highlights
Porphyromonas gingivalis, a gram-negative anaerobe, is thought to be a major causative pathogen of periodontal diseases [1]
It is known that P. gingivalis strains 381 and ATCC 33277 (33277) express aberrant long FimA fimbriae over a few micrometers in length, and we demonstrated that this was attributable to FimB deficiency [8]
It is reported that the loss of fimX and pgmA abolishes or decreases FimA protein production [12], but it is still unclear whether they play a vital role in polymerization of FimA
Summary
Porphyromonas gingivalis, a gram-negative anaerobe, is thought to be a major causative pathogen of periodontal diseases [1]. P. gingivalis generally expresses two distinct fimbriae, called FimA and Mfa fimbriae, which are composed of polymerized FimA and Mfa proteins encoded by the fimA and mfa genes, respectively [2]. Even when FimB-E were deficient, FimA protein was produced and polymerized to form the fimbrial structure, the amount of fimbriae decreased [10,11]. The upstream gene fimX was reported to lead drastic reduction in fimA transcription [12], whereas a mutation in pgmA considerably decreased it [12], indicating a principal role for them in the regulation cascade of FimA protein expression. With regard to type IV, since it was reported that FimA protein was not polymerized into fimbriae in W83 even when it was forcedly produced in the cell through gene manipulation [25], another type IV strain HG564. Purified fimbriae were denatured at various heating temperatures, and subjected to SDS-PAGE analysis with
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