The correlation of113Cd NMR and111mCd PAC spectroscopies provides a powerful approach for the characterization of the structure of CdII-substituted ZnII proteins

Olga Iranzo, Tamas Jakusch, Kyung Hoon Lee, Lars Hemmingsen, Vincent L. Pecoraro

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

CdII has been used as a probe of zinc metalloenzymes and proteins because of the spectroscopic silence of ZnII. One of the most commonly used spectroscopic techniques is 113Cd NMR; however, in recent years 111mCd Perturbed Angular Correlation spectroscopy (111mCd PAC) has also been shown to provide useful structural, speciation and dynamics information on CdII complexes and biomolecules. In this article, we show how the joint use of 113Cd NMR and 111mCd PAC spectroscopies can provide detailed information about the CdII environment in thiolate-rich proteins. Specifically we show that the 113CdNMR chemical shifts observed for CdII in the designed TRI series (TRI = Ac-G-(LKALEEK)4G-NH2) of peptides vary depending on the proportion of trigonal planar CdS3 and pseudotetrahedral CdS3O species present in the equilibrium mixture. PAC spectra are able to quantify these mixtures. When one compares the chemical shift range for these peptides (from δ=570 to 700 ppm), it is observed that CdS3 species have δ 675-700 ppm, CdS3O complexes fall in the range δ 570-600 ppm and mixtures of these forms fall linearly between these extremes. If one then determines the pKa2 values for CdII complexation [pKa2 is for the reaction Cd[(peptide-H)2(peptide)]+→Cd-(peptide) 3- + 2H+] and compares these to the observed chemical shift for the Cd(peptide)3- complexes, one finds that there is also a direct linear correla tion. Thus, by determining the chemical shift value of these species, one can directly assess the metal-binding affinity of the construct. This illustrates how proteins may be able to fine tune metal-binding affinity by destabilizing one metallospecies with respect to another. More important, these studies demonstrate that one may have a broad 113CdNMR chemical shift range for a chemical species (e.g., CdS 3O) which is not necessarily a reflection of the structural diversity within such a four-coordinate species, but rather a consequence of a fast exchange equilibrium between two related species (e.g., CdS3O and CdS3). This could lead to reinterpretation of the assignments of cadmium-protein complexes and may impact the application of CdII as a probe of ZnII sites in biology.

Original languageEnglish
Pages (from-to)3761-3772
Number of pages12
JournalChemistry - A European Journal
Volume15
Issue number15
DOIs
Publication statusPublished - Apr 6 2009

Keywords

  • Cadmium
  • Metallopeptides
  • NMR spectroscopy
  • Zinc proteins

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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