Porphyromonas gingivalis
, 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
Escherichia coli
Fur box, but the wild-type phenotype of the mutant Δ
pgfur
strain was restored partially when expression of the
ecfur
gene was induced from the native
pgfur
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
pgfur
strain. The modified proteins were produced in
E. coli
at significantly lower levels, were highly unstable, and did not bind zinc. The
pgfur
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
2+
, Zn
2+
, or Mn
2+
on
pgfur
gene expression was observed. Two chromosomal mutant strains producing protein lacking 4 (
pgfur
Δ
4aa
) or 13 (
pgfur
Δ
13aa
) C-terminal amino acid residues were examined in regard to importance of the C-terminal lysine-rich region. The
pgfur
Δ
13aa
strain showed a phenotype typical for the mutant Δ
pgfur
strain, but both the wild-type PgFur protein and its truncated version bound zinc with similar ability. The Δ
pgfur
mutant strain produced higher amounts of HmuY protein compared with the wild-type strain, suggesting compromised regulation of its expression. Potential PgFur ligands, Fe
2+
, Mn
2+
, Zn
2+
, PPIX, or serum components, did not influence HmuY production in the Δ
pgfur
mutant strain. The mutant
pgfur
Δ
4aa
and
pgfur
Δ
13aa
strains exhibited affected HmuY protein production. PgFur, regardless of the presence of the C-terminal lysine-rich region, bound to the
hmu
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
in vivo
multilayer regulatory net...