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首页> 外文期刊>Chemistry: A European journal >The importance of the long type 1 copper-binding loop of nitrite reductase for structure and function
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The importance of the long type 1 copper-binding loop of nitrite reductase for structure and function

机译：亚硝酸还原酶长1型铜结合环对结构和功能的重要性

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摘要

The long 15-residue type 1 copper-binding loop of nitrite reductase has been replaced with that from the cupredoxin amicyanin (7 residues). This sizable loop contraction does not have a significant effect on the spectroscopy, and therefore, the structures of both the type 1 and type 2 Cu-II sites. The crystal structure of this variant with Zn-II at both the type 1 and type 2 sites has been determined. The coordination geometry of the type 2 site is almost identical to that found in the wild-type protein. However, the structure of the type 1 centre changes significantly upon metal substitution, which is an unusual feature for this class of site. The positions of most of the coordinating residues are altered of which the largest difference was observed for the coordinating His residue in the centre of the mutated loop. This ligand moves away from the active site, which results in a more open metal centre with a coordinating water molecule. Flexibility has been introduced into this region of the protein. The 200 mV increase in the reduction potential of the type 1 copper site indicates that structural changes upon reduction must stabilise the cuprous form. The resulting unfavourable driving force for electron transfer between the two copper sites, and an increased reorganisation energy for the type 1 centre, contribute to the loop variant having very little nitrite reductase activity. The extended type 1 copper-binding loop of this enzyme makes a number of interactions that are important for maintaining quaternary structure.
机译：亚硝酸还原酶的15个残基长的1型铜结合环已被铜氧还蛋白花青素（7个残基）所取代。这种可观的环收缩对光谱没有显着影响，因此对1型和2型Cu-II位点的结构都没有影响。已经确定了在1型和2型位点均具有Zn-II的该变体的晶体结构。 2型位点的配位几何几乎与野生型蛋白质中的配位几何相同。但是，第1类中心的结构在金属取代后发生了显着变化，这是此类场所的不寻常特征。大多数配位残基的位置都发生了改变，其中在突变环的中心观察到最大的配位His残基差异。该配体从活性位点移开，从而导致金属中心更开放，并带有配位水分子。灵活性已被引入该蛋白质的这一区域。 1型铜位的还原电位增加200 mV，表明还原后的结构变化必须稳定亚铜形式。对于两个铜位之间的电子转移产生的不利驱动力，以及对于1型中心的重组能量的增加，导致具有亚硝酸盐还原酶活性非常低的环变体。该酶的延伸的1型铜结合环产生许多相互作用，这些相互作用对于维持四级结构很重要。

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