Mevarech M, Frolow F, Gloss L M
Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
Biophys Chem. 2000 Aug 30;86(2-3):155-64. doi: 10.1016/s0301-4622(00)00126-5.
Halophilic enzymes, while performing identical enzymatic functions as their non-halophilic counterparts, have been shown to exhibit substantially different properties, among them the requirement for high salt concentrations, in the 1-4 M range, for activity and stability, and a high excess of acidic over basic amino residues. The following communication reviews the functional and structural properties of two proteins isolated from the extremely halophilic archaeon Haloarcula marismortui: the enzyme malate-dehydrogenase (hMDH) and the 2Fe-2S protein ferredoxin. It is argued that the high negative surface charge of halophilic proteins makes them more soluble and renders them more flexible at high salt concentrations, conditions under which non-halophilic proteins tend to aggregate and become rigid. This high surface charge is neutralized mainly by tightly bound water dipoles. The requirement of high salt concentration for the stabilization of halophilic enzymes, on the other hand, is due to a low affinity binding of the salt to specific sites on the surface of the folded polypeptide, thus stabilizing the active conformation of the protein.
嗜盐酶虽然与非嗜盐酶执行相同的酶促功能，但已显示出具有显著不同的特性，其中包括在1-4M范围内需要高盐浓度来保持活性和稳定性，以及酸性氨基酸残基比碱性氨基酸残基过量很多。以下交流内容综述了从极端嗜盐古菌盐沼盐杆菌中分离出的两种蛋白质的功能和结构特性：苹果酸脱氢酶（hMDH）和2Fe-2S蛋白铁氧化还原蛋白。有人认为，嗜盐蛋白质的高负表面电荷使其在高盐浓度下更易溶解且更具柔韧性，而在这种条件下非嗜盐蛋白质往往会聚集并变得僵硬。这种高表面电荷主要由紧密结合的水偶极子中和。另一方面，嗜盐酶稳定需要高盐浓度是由于盐与折叠多肽表面特定位点的低亲和力结合，从而稳定了蛋白质的活性构象。
