The Limitations of X-ray Absorption Spectroscopy for Determining the Structure of Zinc Sites in Proteins. When Is a Tetrathiolate Not a Tetrathiolate?

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• 作者：Kimber Clark-Baldwin ; David L. Tierney ; Nandakumar Govindaswamy ; Eric S. Gruff ; Chongwoo Kim ; Jeremy Berg ; Stephen A. Koch ; and James E. Penner-Hahn
• 刊名：Journal of the American Chemical Society
• 出版年：1998
• 出版时间：August 26, 1998
• 年：1998
• 卷：120
• 期：33
• 页码：8401 - 8409
• 全文大小：252K
• 年卷期：v.120,no.33(August 26, 1998)
• ISSN：1520-5126

文摘

X-ray absorption fine structure (XAFS) spectra have been measured for a series of structurallycharacterized zinc model complexes that mimic the zinc sites found in metalloproteins. These include bothinorganic zinc coordination complexes and small zinc binding peptides. These data have been analyzed todetermine the extent to which Zn XAFS can be used to determine reliably the ligation environment of thezinc. Because Zn-N and Zn-S XAFS oscillations are nearly out of phase over the accessible energy range,it is difficult to determine the relative number of sulfur and nitrogen scatterers, and in some cases, it is evendifficult to determine whether a low-Z (N or O) ligand is bound in the presence of high-Z (S) ligands. Wedescribe a protocol that, by controlling the number of variable parameters, can be used to obtain an accuratequantitation of the number of low-Z ligands. We also show that two of the variables that are often treated asfreely adjustable parameters, the scale factor and shift in the threshold energy, can lead to erroneous results ifnot carefully controlled.