Micelle-Catalyzed Domain
Swapping in the GlpG Rhomboid
Protease Cytoplasmic Domain
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Abstract
Three-dimensional
domain swapping is a mode of self-interaction
that can give rise to altered functional states and has been identified
as the trigger event in some protein deposition diseases, yet rates
of interconversion between oligomeric states are usually slow, with
the requirement for transient disruption of an extensive network of
interactions giving rise to a large kinetic barrier. Here we demonstrate
that the cytoplasmic domain of the <i>Escherichia coli</i> GlpG rhomboid protease undergoes slow dimerization via domain swapping
and that micromolar concentrations of micelles can be used to enhance
monomer–dimer exchange rates by more than 1000-fold. Detergents
bearing a phosphocholine headgroup are shown to be true catalysts,
with hexadecylphosphocholine reducing the 26 kcal/mol free energy
barrier by >11 kcal/mol while preserving the 5 kcal/mol difference
between monomer and dimer states. Catalysis involves the formation
of a micelle-bound intermediate with a partially unfolded structure
that is primed for domain swapping. Taken together, these results
are the first to demonstrate true catalysis for domain swapping, by
using micelles that work in a chaperonin-like fashion to unfold a
kinetically trapped state and allow access to the domain-swapped form