Dynamic Conformational States Dictate Selectivity toward the Native Substrate in a Substrate-Permissive Acyltransferase

Hydroxycinnamoyl-CoA:shikimate
hydroxycinnamoyltransferase (HCT)
is an essential acyltransferase that mediates flux through plant phenylpropanoid
metabolism by catalyzing a reaction between p-coumaroyl-CoA
and shikimate, yet it also exhibits broad substrate permissiveness in vitro. How do enzymes like HCT avoid functional derailment
by cellular metabolites that qualify as non-native substrates? Here,
we combine X-ray crystallography and molecular dynamics to reveal
distinct dynamic modes of HCT under native and non-native catalysis.
We find that essential electrostatic and hydrogen-bonding interactions
between the ligand and active site residues, permitted by active site
plasticity, are elicited more effectively by shikimate than by other
non-native substrates. This work provides a structural basis for how
dynamic conformational states of HCT favor native over non-native
catalysis by reducing the number of futile encounters between the
enzyme and shikimate.