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Phosphophoryn, an “acidic” biomineralization regulatory protein: Conformational folding in the presence of Cd(II)
Author(s) -
Evans John Spencer,
Chiu Thomas,
Chan Sunney I.
Publication year - 1994
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360341008
Subject(s) - chemistry , divalent , polyelectrolyte , crystallography , nuclear magnetic resonance spectroscopy , circular dichroism , stoichiometry , folding (dsp implementation) , conformational change , macromolecule , stereochemistry , biochemistry , organic chemistry , polymer , electrical engineering , engineering
The divalent cation‐induced protein folding properties of the template macromolecule, bovine dentine phosphophoryn (BDPP), have been examined by 1 H/ 31 P/ 13 C/ 113 Cd‐nmr spectroscopy. Cd(II) was employed, exploiting the sensitivity of 113 Cd‐nmr to ligand‐binding interactions and kinetics. Cation binding was studied over the stoichiometric range of 0–50 : 1 Cd(II) : protein (mole ratio), well below the range of Cd(II) concentration required to induce protein precipitation. The stepwise titration of divalent cation‐depleted phosphophoryn at pH 7.2 in H 2 O/D 2 O with 113 CdCl 2 revealed that (PSer) n , (PSerAsp) n , and (Asp) n polyelectrolyte cation‐binding domains undergo two major transitions in their secondary and tertiary structures: the first transition, occurring between 1 : 10 and 1 : 1 Cd(II) : protein stoichiometry, and the second, between 10 : 1 and 50 : 1. By monitoring the amide NH intensities, 31 P‐nmr chemical shift, and 13 C Asp‐C, resonances, it was concluded that Cd(II) ions exhibit a binding‐site preference for polyelectrolyte cation‐binding domains, in the order\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm (PSer)}_n {\rm > (PSerAsp)}_n {\rm > (Asp)}_n $$\end{document} This preference correlates with the degree of negative charge density for each sequence motif. Accompanying the backbone conformational transitions at the polyelectrolyte regions were conformational transitions in the flanking hinge domains, indicating that the hinge domains participate in the folding of the phosphophoryn molecule as divalent cation binding occurs at the polyelectrolyte domains. We were unsuccessful in detecting phosphophoryn‐bound Cd (11) species by 113 Cd‐nmr because of chemical exchange modulation. However, using a smaller 21‐residue peptide mimetic of phosphophoryn, we have observed three stoichiometric‐dependent 113 Cd resonances that differ in terms of the oxoanion coordination number. Our observation of multiple Cd(II) species in the presence of the peptide supports our contention that Cd(II) has many chemically distinct coordination sites on phosphophoryn, each in multiple equilibria with H 2 O, Cl − , and side‐chain oxoatoms. © 1994 John Wiley & Sons, Inc.