Structure and metal binding properties of ZnuA, a periplasmic zinc transporter from Escherichia coli
Structure and metal binding properties of ZnuA, a periplasmic zinc transporter from Escherichia coli
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DOI：
10.1007/s00775-007-0320-0
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发表时间：
2008-02-01
影响因子：
3
通讯作者：
Rosenzweig, Amy C.
中科院分区：
文献类型：
--
作者：
Yatsunyk, Liliya A.;Easton, J. Allen;Rosenzweig, Amy C.
ZnuA是与大肠杆菌的高亲和力ATP结合盒ZnuABC转运蛋白相关的周质Zn 2+结合蛋白。虽然ZnuA及其同系物的几种结构已经确定，但有关金属离子化学计量，亲和力和特异性以及金属吸收和转移机制的细节仍然不清楚。对E. coli ZnuA（Eco-ZnuA）的载脂蛋白、锌离子结合和钴离子结合形式。ZnZnuA结合至少两种金属离子。第一个，以前在其他结构中观察到的，由Glu 59，His 60，His 143和His 207四面体配位。用Co 2+取代Zn 2+导致在该位点几乎相同的配位几何形状。第二个金属结合位点涉及His 224和几个尚待鉴定的富含His的环的残基，该环是Zn 2+周质金属结合受体所特有的。CoZnuA的电子顺磁共振和X射线吸收光谱数据提供了额外的洞察可能的残基参与这第二个网站。第二个网站也检测到金属分析和圆二色性（CD）滴定。Eco-ZnuA结合Zn 2+（估计Kd < 20 nM）、Co2+、Ni 2+、Cu 2+、Cu+和Cd 2+，但不结合Mn 2+。最后，在晶体结构中观察到的金属结合后的构象变化以及荧光和CD数据表明，只有Zn 2+基本上稳定ZnuA，并可能促进ZnuB的识别和随后的金属转移。
ZnuA is the periplasmic Zn2+-binding protein associated with the high-affinity ATP-binding cassette ZnuABC transporter from Escherichia coli. Although several structures of ZnuA and its homologs have been determined, details regarding metal ion stoichiometry, affinity, and specificity as well as the mechanism of metal uptake and transfer remain unclear. The crystal structures of E. coli ZnuA (Eco-ZnuA) in the apo, Zn2+-bound, and Co2+-bound forms have been determined. ZnZnuA binds at least two metal ions. The first, observed previously in other structures, is coordinated tetrahedrally by Glu59, His60, His143, and His207. Replacement of Zn2+ with Co2+ results in almost identical coordination geometry at this site. The second metal binding site involves His224 and several yet to be identified residues from the His-rich loop that is unique to Zn2+ periplasmic metal binding receptors. Electron paramagnetic resonance and X-ray absorption spectroscopic data on CoZnuA provide additional insight into possible residues involved in this second site. The second site is also detected by metal analysis and circular dichroism (CD) titrations. Eco-ZnuA binds Zn2+ (estimated K-d < 20 nM), Co2+, Ni2+, Cu2+, Cu+, and Cd2+, but not Mn2+. Finally, conformational changes upon metal binding observed in the crystal structures together with fluorescence and CD data indicate that only Zn2+ substantially stabilizes ZnuA and might facilitate recognition of ZnuB and subsequent metal transfer.