Rational Engineering of a Pseudaminic Acid Synthase Enzyme Enables Access to a 3-Fluoro Sugar with Motility Inhibition in Bacterial Pathogens.

We report the rational engineering of a pseudaminic acid synthase (PseI), which enables the first synthesis of a 3-fluorinated pseudaminic acid sugar (3-(eq)-F-Pse5Ac7Ac), potentially establishing a new class of metabolic inhibitors targeting bacterial glycosylation. Pseudaminic acids are ⍺-keto acid sugars essential for O-glycosylation of flagellin in pathogens such as Campylobacter jejuni, where they are critical for motility and virulence. By introducing rational mutations in the PseI active site, we achieve enhanced turnover with unnatural 3-fluoro-phosphoenolpyruvate, facilitating a scalable chemoenzymatic synthesis of the fluorinated sugar. Subsequent treatment of C. jejuni with 3-(eq)-F-Pse5Ac7Ac resulted in a significant, time-dependent reduction in motility, and in vitro studies demonstrated bacterial CMP-pseudaminic acid synthetase enzymes (PseF) can process the fluoro sugar to afford CMP-3-(eq)-F-Pse5Ac7Ac, potentially implicating the fluorinated pseudaminic acid or its glycosyltransferase CMP-donor as an anti-motilin in vivo. This study demonstrates, for the first time, that fluorinated pseudaminic acids can impair bacterial motility, paving the way for anti-virulence strategies in pathogenic bacteria. This anti-motilin approach offers a promising alternative to traditional antibiotics, addressing the urgent need for novel strategies to combat antimicrobial resistance, and could be extended to other bacterial ⍺-keto acid sugars.