X-ray crystal structure of
Vibrio alkaline phosphatase with the non-competitive inhibitor cyclohexylamine.
Biochem Biophys Rep 2020;
24:100830. [PMID:
33102813 PMCID:
PMC7569297 DOI:
10.1016/j.bbrep.2020.100830]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 10/06/2020] [Indexed: 11/13/2022] Open
Abstract
Background
Para-nitrophenyl phosphate, the common substrate for alkaline phosphatase (AP), is available as a cyclohexylamine salt. Here, we report that cyclohexylamine is a non-competitive inhibitor of APs.
Methods
Cyclohexylamine inhibited four different APs. Co-crystallization with the cold-active Vibrio AP (VAP) was performed and the structure solved.
Results
Inhibition of VAP fitted a non-competitive kinetic model (Km unchanged, Vmax reduced) with IC50 45.3 mM at the pH optimum 9.8, not sensitive to 0.5 M NaCl, and IC50 27.9 mM at pH 8.0, where the addition of 0.5 M NaCl altered the inhibition to the level observed at pH 9.8. APs from E. coli and calf intestines were less sensitive to cyclohexylamine, whereas an Antarctic bacterial AP was similar to VAP in this respect. X-ray crystallography at 2.3 Å showed two binding sites, one in the active site channel and another at the surface close to dimer interface. Antarctic bacterial AP and VAP have Trp274 in common in their active-sites, that takes part in binding cyclohexylamine. VAP variants W274A, W274K, and W274H gave IC50 values of 179 mM, 188 mM and 187 mM, respectively, at pH 9.8.
Conclusions
The binding of cyclohexylamine in locations at the dimeric interface and/or in the active site of APs may delay product release or reduce the rate of catalytic step(s) involving conformational changes and intersubunit communications.
General significance
Cyclohexylamine is a common chemical in industries and used as a counterion in substrates for alkaline phosphatase, a clinically important and common enzyme in the biosphere.
Cyclohexylamine inhibits alkaline phosphatase activity non-competitively.
X-ray structure was solved that shows cyclohexylamine bound to alkaline phosphatase at two sites.
Alkaline phosphatases from four different organisms bind cyclohexylamine with varying affinity.
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