title: Proline cis-trans isomers in calbindin D9k observed by X-ray crystallography.
abstract: 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.
authors.affiliation: Department of Molecular Biophysics, University of Lund, Sweden.
authors.forename: L A
authors.initials: LA
authors.lastname: Svensson
authors.forename: E
authors.initials: E
authors.lastname: Thulin
authors.forename: S
authors.initials: S
authors.lastname: Forsén
mesh_terms: D000595:Amino Acid Sequence; D064026:Calbindins; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011392:Proline / Q000737:chemistry*; D064030:S100 Calcium Binding Protein G / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D064026:Calbindins; D064030:S100 Calcium Binding Protein G; D011392:Proline