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Publication Abstract from PubMed

The gamma-class carbonic anhydrases (gamma-CAs) mainly come from methanogens methane-producing bacteria that grow in hot springs and catalyze the interconversion of carbon dioxide and water to bicarbonate and protons. Here, the gamma-CA from Thermus thermophilus HB8 (gamma-TtCA) was expressed and purified, its crystal structure was determined at 2.3 A resolution in space group P1. The asymmetric unit contains two trimers and six catalytic Zn(2+). In general, the fold of the protein is similar to those of homologous enzymes from Geobacillus Kaustophilus, Bacillus Cereus, Methanosarcina Thermophila and others. Each monomer comprises a triangular prism-like structure consisting of a left-handed beta-helix and a C-terminal alpha-helix. The catalytic Zn(2+) bound to three histidines and a phosphate radical in a tetrahedral fashion. It is located at the interface between the two monomers. Inductively coupled plasma mass spectrometry measurements further suggest that the molar ratio of zinc ions and protein molecules is 1:1. The structure revealed a novel different region situated between the left-handed beta-helix and the C-terminal alpha-helix. Compared to previously reported structures, half of the C-terminal alpha-helix was replaced with a long loop in this structure. The purified gamma-TtCA exhibits no significant carbonic anhydrase activity compared to alpha-class carbonic anhydrases. This study provides insight into the structural diversity of gamma-CAs with potential function for gamma-CAs.

Molecular structure of thermostable and zinc-ion-binding gamma-class carbonic anhydrases.,Wang W, Zhang Y, Wang L, Jing Q, Wang X, Xi X, Zhao X, Wang H Biometals. 2019 Apr;32(2):317-328. doi: 10.1007/s10534-019-00190-8. Epub 2019 Mar, 20. PMID:30895492^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.