Li H, Otvos J D
Department of Food Science, North Carolina State University, Raleigh 27695, USA.
Biochemistry. 1996 Nov 5;35(44):13929-36. doi: 10.1021/bi961401n.
Metal displacement reactions of Cd7MT with Ag+ or Cu+ and interprotein metal exchange reactions between Cd7MT and Ag12MT or Cu12MT were studied by 111Cd NMR. Titration of 111Cd7MT with Ag+ indicates that Ag+ binds preferentially to the beta-domain of the protein to form the metal hybrid species, (Cd4)alpha(Ag6)beta MT. Once the beta-domain is filled, additional Ag+ ions displace Cd2+ from the alpha-domain to form (Ag6)alpha(Ag6)beta MT. The metal displacement reaction is cooperative and the two domains react independently of one another. The (Cd4)alpha(Ag6)beta MT hybrid protein is also formed as the major product of direct interprotein metal exchange between Cd7MT and Ag12MT. Cu+ reacts with Cd7MT in a manner similar to Ag+, with addition of 6 equiv of Cu+ leading to preferential formation of (Cd4)alpha(Cu6)beta-MT, and 12 equiv of Cu+ to formation of (Cu6)alpha(Cu6)beta MT. However, unlike Ag+, Cu+ appears to produce intermediate species that may contain mixed-metal clusters. Interprotein metal exchange between Cu12-MT and Cd7MT leads to the net transfer of Cd2+ into the alpha-domain and Cu+ into the beta-domain. The differential affinities of the two domains for monovalent and divalent metal ions plus the availability of facile pathways for metal exchange may be features that enable MT to function simultaneously in the metabolism of different metal ions.
利用111Cd核磁共振研究了Cd7MT与Ag+或Cu+的金属置换反应以及Cd7MT与Ag12MT或Cu12MT之间的蛋白质间金属交换反应。用Ag+滴定111Cd7MT表明，Ag+优先与蛋白质的β结构域结合形成金属杂化物种，即(Cd4)α(Ag6)βMT。一旦β结构域被填满，额外的Ag+离子会从α结构域置换出Cd2+，形成(Ag6)α(Ag6)βMT。金属置换反应是协同的，两个结构域相互独立反应。(Cd4)α(Ag6)βMT杂合蛋白也是Cd7MT与Ag12MT之间直接蛋白质间金属交换的主要产物。Cu+与Cd7MT的反应方式与Ag+类似，加入6当量的Cu+会优先形成(Cd4)α(Cu6)β - MT，加入12当量的Cu+会形成(Cu6)α(Cu6)βMT。然而，与Ag+不同的是，Cu+似乎会产生可能包含混合金属簇的中间物种。Cu12 - MT与Cd7MT之间的蛋白质间金属交换导致Cd2+净转移到α结构域，Cu+净转移到β结构域。两个结构域对单价和二价金属离子的不同亲和力以及金属交换的便捷途径可能是使MT能够在不同金属离子的代谢中同时发挥作用的特征。
