PgFur Is a Member of a Novel Fur Subfamily With Non-canonical Function.

, a keystone pathogen of chronic periodontitis, uses ferric uptake regulator homolog (PgFur) to regulate production of virulence factors. This study aimed to characterize PgFur protein in regard to its structure-function relationship. We experimentally identified the 5' mRNA sequence encoding the 171-amino-acid-long PgFur protein in the A7436 strain and examined this PgFur version as a full-length protein. PgFur protein did not bind to the canonical Fur box, but the wild-type phenotype of the mutant Δ strain was restored partially when expression of the gene was induced from the native promoter. The full-length PgFur protein contained one zinc atom per protein monomer, but did not bind iron, manganese, or heme. Single cysteine substitutions of CXXC motifs resulted in phenotypes similar to the mutant Δ strain. The modified proteins were produced in at significantly lower levels, were highly unstable, and did not bind zinc. The gene was expressed at the highest levels in bacteria cultured for 24 h in the absence of iron and heme or at higher levels in bacteria cultured for 10 h in the presence of protoporphyrin IX source. No influence of high availability of Fe, Zn, or Mn on gene expression was observed. Two chromosomal mutant strains producing protein lacking 4 (Δ) or 13 (Δ) C-terminal amino acid residues were examined in regard to importance of the C-terminal lysine-rich region. The Δ strain showed a phenotype typical for the mutant Δ strain, but both the wild-type PgFur protein and its truncated version bound zinc with similar ability. The Δ mutant strain produced higher amounts of HmuY protein compared with the wild-type strain, suggesting compromised regulation of its expression. Potential PgFur ligands, Fe, Mn, Zn, PPIX, or serum components, did not influence HmuY production in the Δ mutant strain. The mutant Δ and Δ strains exhibited affected HmuY protein production. PgFur, regardless of the presence of the C-terminal lysine-rich region, bound to the operon promoter. Our data suggest that cooperation of PgFur with partners/cofactors and/or protein/DNA modifications would be required to accomplish its role played in an multilayer regulatory network.