cAMP-independent Crp homolog adds to the multi-layer regulatory network in Porphyromonas gingivalis

Michał Śmiga ^* Ewa Roszkiewicz Paulina Ślęzak Michał Tracz Teresa Olczak

• University of Wrocław, Wrocław, Poland

Porphyromonas gingivalis encodes three CRP/FNR superfamily proteins: HcpR, PgRsp, and Crp Pg , with Crp Pg similar to cAMP-sensing proteins but not classified into known families. This study investigates the role of Crp Pg in regulating the expression of factors essential for P. gingivalis virulence in A7436 and ATCC 33277 strains. Key findings in the Δcrp Pg mutant strain include up-regulated mfa1-5 and rgpA genes and down-regulated trxA, soxR, and ustA genes. While crp Pg inactivation does not affect growth in liquid culture media, it impairs biofilm formation and enhances adhesion to and invasion of gingival keratinocytes. Crp Pg binds directly to its own and mfa promoters without interacting with cyclic nucleotides or di-nucleotides. Its three-dimensional structure, resembling E. coli Crp in complex with cAMP and DNA, suggests that Crp Pg functions as a global regulator independently of cAMP binding. The highest crp Pg expression in the early exponential growth phase declines as cell density and metabolic conditions change over time, suggesting regulatory function depending on the Crp Pg protein amount. By controlling the shift from planktonic to biofilm lifestyle, Crp Pg may play a role in pathogenicity. Regulating the expression of virulence factors required for host cell invasion and intracellular replication, Crp Pg may help P. gingivalis evade immune responses.