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Abstract：
Calgranulin C performs antimicrobial activity in the human immune response by sequestering Zn(II). This biological function is afforded with the aid of two structurally distinct Ca(II)-binding EF hand motifs, wherein one of which bears an unusual amino acid sequence. Here, we utilize solution state NMR relaxation measurements to investigate the mechanism of Ca(II)-modulated enhancement of Zn(II) sequestration by calgranulin C. Using C13 /N15 CPMG dispersion experiments we have measured pH-dependent major and minor state populations exchanging on micro-to-millisecond timescale. This conformational exchange takes place exclusively in the Ca(II)-bound state and can be mapped to residues located in the EF-I loop and the linker between the tandem EF hands. Molecular dynamics (MD) simulations spanning nano-to-microsecond timescale offer insights into the role of pH-dependent electrostatic interactions in EF-hand dynamics. Our results suggest a pH-regulated dynamic equilibrium of conformations that explore a range of \"closed\" and partially \"open\" sidechain configurations within the Zn(II) binding site. We propose a novel mechanism by which Ca(II) binding to a non-canonical EF loop regulates its flexibility and tunes the antimicrobial activity of calgranulin C.
摘要：
钙粒蛋白C通过螯合Zn（II）在人类免疫反应中发挥抗菌活性。这种生物学功能是在两个结构上不同的Ca（II）结合EF手基序的帮助下提供的，其中一个带有不寻常的氨基酸序列。这里,我们利用溶液状态NMR弛豫测量来研究钙颗粒蛋白C对Ca（II）调制的Zn（II）螯合增强的机理。使用C13/N15CPMG分散实验，我们测量了pH依赖性的主要和次要状态种群在微到毫秒时间尺度上的交换。这种构象交换仅在Ca（II）结合状态下发生，并且可以映射到位于EF-I环和串联EF手之间的接头中的残基。跨越纳米到微秒时间尺度的分子动力学（MD）模拟提供了对pH依赖性静电相互作用在EF手动力学中的作用的见解。我们的结果表明，构象的pH调节动态平衡可探索Zn（II）结合位点内的一系列“封闭”和部分“开放”侧链构型。
