Park I S, Hausinger R P
Department of Microbiology, Michigan State University, East Lansing 48824.
Science. 1995 Feb 24;267(5201):1156-8. doi: 10.1126/science.7855593.
Assembly of protein metallocenters is not well understood. Urease offers a tractable system for examination of this process. Formation of the urease metallocenter in vivo is known to require four accessory proteins: UreD, postulated to be a urease-specific molecular chaperone; UreE, a nickel(II)-binding protein; and UreF and UreG, of unknown function. Activation of purified Klebsiella aerogenes urease apoprotein was accomplished in vitro by providing carbon dioxide (half-maximal activation at approximately 0.2 percent carbon dioxide) in addition to nickel ion. Activation coincided with carbon dioxide incorporation into urease in a pH-dependent reaction (pKa > or = 9, where Ka is the acid constant). The concentration of carbon dioxide also affected the amount of activation of UreD-urease apoprotein complexes. These results suggest that carbon dioxide binding to urease apoprotein generates a ligand that facilitates productive nickel binding.
蛋白质金属中心的组装过程尚未得到充分理解。脲酶为研究这一过程提供了一个易于处理的系统。已知在体内脲酶金属中心的形成需要四种辅助蛋白：UreD，推测为脲酶特异性分子伴侣；UreE，一种镍（II）结合蛋白；以及功能未知的UreF和UreG。通过在体外除提供镍离子外还提供二氧化碳（在约0.2%二氧化碳浓度下达到半数最大激活），实现了纯化的产气克雷伯菌脲酶脱辅基蛋白的激活。激活与二氧化碳在pH依赖性反应（pKa≥9，其中Ka为酸常数）中掺入脲酶同时发生。二氧化碳浓度也影响UreD-脲酶脱辅基蛋白复合物的激活量。这些结果表明，二氧化碳与脲酶脱辅基蛋白的结合产生了一种促进有效镍结合的配体。
