Many bacteria require ATP binding cassette (ABC) transporters for the import of the essential metal zinc from limited environments. These systems rely on a periplasmic or cell-surface solute binding protein (SBP) to bind zinc with high affinity and specificity. AztABCD is one such zinc transport system recently identified in a large group of diverse bacterial species. In addition to a classical SBP (AztC), the operon also includes a periplasmic metallochaperone (AztD) shown to transfer zinc directly to AztC. Crystal structures of both proteins from Paracoccus denitrificans have been solved and suggest several structural features on each that may be important for zinc binding and transfer. Here we determine zinc binding affinity, dissociation kinetics, and transfer kinetics for several deletion mutants as well as a crystal structure for one of them. The results indicate specific roles for loop structures on AztC and an N-terminal motif on AztD in zinc binding and transfer. These data are consistent with a structural transfer model proposed previously and provide further mechanistic insight into the processes of zinc binding and transfer.

中文翻译：

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在AztABCD锌转运系统中介导锌结合和转移的结构特征。

许多细菌需要ATP结合盒（ABC）转运蛋白才能从有限的环境中导入必需的金属锌。这些系统依靠周质或细胞表面溶质结合蛋白（SBP）以高亲和力和特异性结合锌。AztABCD是最近在一大批不同细菌物种中发现的一种此类锌转运系统。除了经典的SBP（AztC），操纵子还包括周质金属陪伴酮（AztD），可将锌直接转移到AztC。脱氮副球菌的两种蛋白质的晶体结构已解决，并提出了对锌结合和转移可能很重要的几种结构特征。在这里，我们确定几个缺失突变体以及其中之一的晶体结构的锌结合亲和力，解离动力学和转移动力学。结果表明AztC上的环结构和AztD的N端基序在锌结合和转移中的特定作用。这些数据与先前提出的结构转移模型相一致，并提供了对锌结合和转移过程的进一步机械性见解。