Somalinga Vijayakumar, Foss Emily, Grunden Amy M
Department of Biological & Biomedical Sciences, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, OK 73096, USA.
Department of Plant and Microbial Biology, North Carolina State University, 4550A Thomas Hall, Campus Box 7612, Raleigh, NC 27695, USA.
AIMS Microbiol. 2023 Jun 19;9(3):540-553. doi: 10.3934/microbiol.2023028. eCollection 2023.
Prokaryotic α-carbonic anhydrases (α-CA) are metalloenzymes that catalyze the reversible hydration of CO to bicarbonate and proton. We had reported the first crystal structure of a pyschrohalophilic α-CA from a deep-sea bacterium, SS9. In this manuscript, we report the first biochemical characterization of α-CA (PprCA) which revealed several catalytic properties that are atypical for this class of CA's. Purified PprCA exhibited maximal catalytic activity at psychrophilic temperatures with substantial decrease in activity at mesophilic and thermophilic range. Similar to other α-CA's, Ppr9A showed peak activity at alkaline pH (pH 11), although, PprCA retained 88% of its activity even at acidic pH (pH 5). Exposing PprCA to varying concentrations of oxidizing and reducing agents revealed that N-terminal cysteine residues in PprCA may play a role in the structural stability of the enzyme. Although inefficient in CO hydration activity under mesophilic and thermophilic temperatures, PprCA exhibited salt-dependent thermotolerance and catalytic activity under extreme halophilic conditions. Similar to other well-characterized α-CA's, PprCA is also inhibited by monovalent anions even at low concentrations. Finally, we demonstrate that PprCA accelerates CO biomineralization to calcium carbonate under alkaline conditions.
原核α-碳酸酐酶（α-CA）是一种金属酶，可催化二氧化碳可逆水合生成碳酸氢根和质子。我们曾报道过来自深海细菌SS9的嗜冷α-碳酸酐酶的首个晶体结构。在本论文中，我们报道了α-碳酸酐酶（PprCA）的首次生化特性研究，结果揭示了这类碳酸酐酶一些非典型的催化特性。纯化后的PprCA在嗜冷温度下表现出最大催化活性，而在中温和嗜热温度范围内活性大幅下降。与其他α-碳酸酐酶类似，Ppr9A在碱性pH（pH 11）时活性达到峰值，不过，即使在酸性pH（pH 5）时，PprCA仍保留88%的活性。将PprCA暴露于不同浓度的氧化剂和还原剂中发现，PprCA的N端半胱氨酸残基可能对该酶的结构稳定性起作用。尽管在中温和嗜热温度下PprCA的二氧化碳水合活性较低，但在极端嗜盐条件下它表现出盐依赖性耐热性和催化活性。与其他已充分表征的α-碳酸酐酶类似，PprCA即使在低浓度下也会受到单价阴离子的抑制。最后，我们证明PprCA在碱性条件下可加速二氧化碳生物矿化形成碳酸钙。
