# Structural and Biochemical Characterization of Fusobacterium nucleatum Enoyl-ACP Reductase II (FabK) Reveals the Basis for Bacterial Species-Specific Inhibition

## TL;DR

This study explores the structure and function of a key enzyme in the bacterium Fusobacterium nucleatum, offering insights for designing targeted antibiotics.

## Contribution

The paper provides the first detailed structural and biochemical characterization of FnFabK, enabling species-specific drug design.

## Key findings

- FnFabK inhibitors show low to submicromolar activity with selectivity over other bacterial FabK homologues.
- Crystallographic analysis reveals unique structural features of FnFabK's active site.
- The findings validate FnFabK as a target for narrow-spectrum antibacterial agents.

## Abstract

Fusobacterium
nucleatum is a Gram-negative
anaerobic bacterium ubiquitous in the oral cavity and increasingly
recognized for its involvement in diverse clinical conditions, including
periodontal disease, inflammatory bowel disease, premature birth,
and several forms of cancer. These associations highlight the need
for narrow-spectrum antibacterial agents directed against F. nucleatum to avoid disruption of beneficial microflora
and limit the rise of antibiotic resistance. Recent studies have identified
the fusobacterial fatty acid synthesis pathway (FAS-II) enzyme, enoyl-acyl
carrier protein (ACP) reductase, FnFabK, as an essential
and promising target for selective antibacterial intervention. However,
there is a lack of detailed structural information, which has hindered
the validation of FnFabK’s druggability and
the discovery of new inhibitors. Here, we present a comprehensive
characterization of FnFabK, including its cocrystal
structure solved at 2.25 Å resolution and its biochemical and
biophysical interactions with a series of potent small-molecule inhibitors.
Our analyses revealed that these inhibitors display low to submicromolar
activity against FnFabK, with notable selectivity
and differential activity when tested against FabK homologues from
other bacterial pathogens. Importantly, the unique structural features
of the FnFabK active site, elucidated through these
crystallographic studies, provide a mechanistic basis for species-specific
inhibition. These findings not only validate FnFabK
as a druggable target but also furnish critical insights into the
design of next-generation narrow-spectrum antibacterial agents.