School of Biological Science, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore.
Department of NEUROFARBA, Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Firenze, Italy.
Acta Crystallogr D Struct Biol. 2020 Jul 1;76(Pt 7):676-686. doi: 10.1107/S2059798320007202. Epub 2020 Jun 30.
Carbonic anhydrases (CAs) are a well characterized family of metalloenzymes that are highly efficient in facilitating the interconversion between carbon dioxide and bicarbonate. Recently, CA activity has been associated with the LCIB (limiting CO-inducible protein B) protein family, which has been an interesting target in aquatic photosynthetic microorganisms. To gain further insight into the catalytic mechanism of this new group of CAs, the X-ray structure of a highly active LCIB homolog (PtLCIB3) from the diatom Phaeodactylum tricornutum was determined. The CA activities of PtLCIB3, its paralog PtLCIB4 and a variety of their mutants were also measured. It was discovered that PtLCIB3 has a classic β-CA fold and its overall structure is highly similar to that of its homolog PtLCIB4. Subtle structural alterations between PtLCIB3 and PtLCIB4 indicate that an alternative proton-shuttle cavity could perhaps be one reason for their remarkable difference in CA activity. A potential alternative proton-shuttle route in the LCIB protein family is suggested based on these results.
碳酸酐酶（CA）是一类经过充分研究的金属酶家族，能够高效地促进二氧化碳和碳酸氢盐之间的相互转化。最近，CA 活性与 LCIB（限制 CO 诱导蛋白 B）蛋白家族相关联，该家族是水生光合微生物中的一个有趣靶点。为了更深入地了解这组新型 CA 的催化机制，测定了来自双鞭甲藻的高活性 LCIB 同源物（PtLCIB3）的 X 射线结构。还测量了 PtLCIB3、其旁系同源物 PtLCIB4 及其各种突变体的 CA 活性。结果发现，PtLCIB3 具有经典的β-CA 折叠，其整体结构与同源物 PtLCIB4 非常相似。PtLCIB3 和 PtLCIB4 之间的细微结构差异表明，替代质子穿梭腔可能是它们在 CA 活性方面显著差异的原因之一。根据这些结果，提出了 LCIB 蛋白家族中潜在的替代质子穿梭途径。
