Sites for Dynamic Protein-Carbohydrate Interactions of O- and C-Linked Mannosides on the E. coli FimH Adhesin

Abstract

Antagonists of the <i>Escherichia coli</i> type-1 fimbrial adhesin FimH are recognized as attractive alternatives for antibiotic therapies and prophylaxes against acute and recurrent bacterial infections. In this study α-d-mannopyranosides <i>O</i>- or <i>C</i>-linked with an alkyl, alkene, alkyne, thioalkyl, amide, or sulfonamide were investigated to fit a hydrophobic substituent with up to two aryl groups within the tyrosine gate emerging from the mannose-binding pocket of FimH. The results were summarized into a set of structure-activity relationships to be used in FimH-targeted inhibitor design: alkene linkers gave an improved affinity and inhibitory potential, because of their relative flexibility combined with a favourable interaction with isoleucine-52 located in the middle of the tyrosine gate. Of particular interest is a <i>C</i>-linked mannoside, alkene-linked to an <i>ortho-</i>substituted biphenyl that has an affinity similar to its <i>O</i>-mannosidic analog but superior to its <i>para-</i>substituted analog. Docking of its high-resolution NMR solution structure to the FimH adhesin indicated that its ultimate, <i>ortho</i>-placed phenyl ring is able to interact with isoleucine-13, located in the clamp loop that undergoes conformational changes under shear force exerted on the bacteria. Molecular dynamics simulations confirmed that a subpopulation of the <i>C</i>-mannoside conformers is able to interact in this secondary binding site of FimH.