Systematic Mapping of Homoserine Lactone and Cyclodextrin Binding Strengths — Effects of Structural Features

Binding of homoserine lactone (HSL) signaling molecules used by Gram-negative bacteria with native and substituted cyclodextrin (CD) host molecules was mapped. Between differently substituted HSLs with different alkyl chain lengths, chain length governed binding affinity. Between α-CD and β-CDs, the wider β-CD cavity was found to be more tolerant of substitutions in terms of binding constant.

Abstract

Directing the collective behavior of bacteria is important for various applications in chemical bioproduction, water treatment, and antibiofilm solutions. A potential approach to such control mechanisms lies in sequestering signal molecules (autoinducers) by macrocyclic host molecules that lower the effective concentration of the former, modulating bacterial signaling. Cyclodextrins (CD) — one of the best-established families of hosts — have been shown to bind homoserine lactones (HSL) acting as autoinducers, but with a focus limited to shorter (≤ 8 carbons) tailed molecules and β-CD. Here, we have systematically mapped binding affinities for HSLs of three different tail lengths and with different 3-site substituents (used for signal differentiation), with native and substituted α- and β-CDs. The HSL alkyl chain length has the most influence on affinity, although the 3-substitution also slightly affects the binding constant. Little difference between native CDs was observed, but the binding ability of α-CD was more susceptible to even minute substitutions. The wider β-CD core could be substituted with greater modularity without impairing HSL binding ability. The results constitute an initial chemical toolbox to be applied in guiding host design for HSL sequestering in, for example, therapeutic applications, but also in constructing systems for the modulation of bacterial collective behavior.

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