posted on 2021-10-11, 16:08authored byJohan Pääkkönen, Leena Penttinen, Martina Andberg, Anu Koivula, Nina Hakulinen, Juha Rouvinen, Janne Jänis
Caulobacter
crescentus xylonolactonase (Cc XylC, EC
3.1.1.68) catalyzes an intramolecular ester
bond hydrolysis over a nonenzymatic acid/base catalysis. Cc XylC is a member of the SMP30 protein family, whose members have
previously been reported to be active in the presence of bivalent
metal ions, such as Ca2+, Zn2+, and Mg2+. By native mass spectrometry, we studied the binding of several
bivalent metal ions to Cc XylC and observed that
it binds only one of them, namely, the Fe2+ cation, specifically
and with a high affinity (Kd = 0.5 μM),
pointing out that Cc XylC is a mononuclear iron protein.
We propose that bivalent metal cations also promote the reaction nonenzymatically
by stabilizing a short-lived bicyclic intermediate on the lactone
isomerization reaction. An analysis of the reaction kinetics showed
that Cc XylC complexed with Fe2+ can speed
up the hydrolysis of d-xylono-1,4-lactone by 100-fold and
that of d-glucono-1,5-lactone by 10-fold as compared to the
nonenzymatic reaction. To our knowledge, this is the first discovery
of a nonheme mononuclear iron-binding enzyme that catalyzes an ester
bond hydrolysis reaction.