Proline cis-trans isomers in calbindin D9k observed by X-ray crystallography.
In a structure of recombinant bovine calbindin D9k, determined crystallographically to 1.6 A resolution, a proline in mixed, approximately equally populated, cis and trans conformation is observed. Isomers of this kind have not been reported in structure determinations of calbindin D9k to 2.3 A resolution or in any other crystallographically determined protein structure. The cis-trans isomerization occurs at the peptide bond between Gly42 and Pro43, which is in agreement with results from two-dimensional 1H nuclear magnetic resonance spectroscopy experiments on solutions of calbindin D9k. Alternative backbone stretches have been modeled and refined by stereochemical restrained least-squares refinement for the segment Lys41 to Pro43. The final R-value was 0.188. The structural perturbations accompanying the cis-trans isomerization are found to be very localized. The largest positional differences are observed at residue Gly42, in which the alternative positions of the oxygen atom are 3.6 A apart.[1]References
- Proline cis-trans isomers in calbindin D9k observed by X-ray crystallography. Svensson, L.A., Thulin, E., Forsén, S. J. Mol. Biol. (1992) [Pubmed]
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