Conformational stability of the bacterial adhesin, FimH, with an
inactivating mutation
Abstract
Allostery governing two conformational states is one of the proposed
mechanisms for catch-bond behavior in adhesion proteins. In FimH, a
catch-bond protein expressed by pathogenic bacteria, separation of two
domains disrupts inhibition by the pili domain. Thus, tensile force can
induce a conformational change in the lectin domain, from an inactive
state to an active state with high affinity. To better understand
allosteric inhibition in two-domain FimH (H2 inactive), we use molecular
dynamics simulations to study the lectin domain alone, which has high
affinity (HL active), and also the lectin domain stabilized in the
low-affinity conformation by an Arg-60-Pro mutation (HL mutant). Because
ligand-binding induces an allostery-like conformational change in HL
mutant, this more experimentally tractable version has been proposed as
a “minimal model” for FimH. We find that HL mutant has larger backbone
fluctuations than both H2 inactive and HL active, at the binding pocket
and allosteric interdomain region. We use an internal coordinate system
of dihedral angles to identify protein regions with differences in
backbone and sidechain dynamics beyond the putative allosteric pathway
sites. By characterizing HL mutant dynamics for the first time, we
provide additional insight into the transmission of allosteric
information across the lectin domain and build upon structural and
thermodynamic data in the literature to further support the use of HL
mutant as a “minimal model.” Understanding how to alter protein
dynamics to prevent the allosteric conformational change may guide drug
development to prevent infection by blocking FimH adhesion.