Xylonolactonase from Caulobacter crescentus Is a Mononuclear Nonheme Iron Hydrolase

• Published in: Biochemistry (Easton) 2021-10, Vol.60 (41), p.3046-3049
• Main Authors: Pääkkönen, Johan, Penttinen, Leena, Andberg, Martina, Koivula, Anu, Hakulinen, Nina, Rouvinen, Juha, Jänis, Janne
• Format: Article
• Language: English
• Subjects: Communication
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/acs.biochem.1c00249

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 (K d = 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.