Structural characterization ofPorphyromonas gingivalisenoyl-ACP reductase II (FabK)

Abstract

Enoyl-acyl carrier protein (ACP) reductase II (FabK) is a critical rate-limiting enzyme in the bacterial type II fatty-acid synthesis (FAS II) pathway. FAS II pathway enzymes are markedly disparate from their mammalian analogs in the FAS I pathway in both structure and mechanism. Enzymes involved in bacterial fatty-acid synthesis represent viable drug targets for Gram-negative pathogens, and historical precedent exists for targeting them in the treatment of diseases of the oral cavity. The Gram-negative organismPorphyromonas gingivalisrepresents a key causative agent of the costly and highly prevalent disease known as chronic periodontitis, and exclusively expresses FabK as its enoyl reductase enzyme in the FAS-II pathway. Together, these characteristics distinguishP. gingivalisFabK (PgFabK) as an attractive and novel narrow-spectrum antibacterial target candidate.PgFabK is a flavoenzyme that is dependent on FMN and NADPH as cofactors for the enzymatic reaction, which reduces the enoyl substrateviaa ping-pong mechanism. Here, the structure of thePgFabK enzyme as determined using X-ray crystallography is reported to 1.9 Å resolution with endogenous FMN fully resolved and the NADPH cofactor partially resolved.PgFabK possesses a TIM-barrel motif, and all flexible loops are visible. The determined structure has allowed insight into the structural basis for the NADPH dependence observed inPgFabK and the role of a monovalent cation that has been observed in previous studies to be stringently required for FabK activity. ThePgFabK structure and the insights gleaned from its analysis will facilitate structure-based drug-discovery efforts towards the prevention and treatment ofP. gingivalisinfection.