1osa
From Proteopedia
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CRYSTAL STRUCTURE OF RECOMBINANT PARAMECIUM TETRAURELIA CALMODULIN AT 1.68 ANGSTROMS RESOLUTION
Overview
The crystal structure of the recombinant calmodulin from Paramecium, tetraurelia (rPCaM, M(r) = 16 700, 148 residues) has been determined at, 1.68 A resolution. X-ray intensity data were collected at 263 K using a, Siemens-Nicolet area detector and Cu Kalpha radiation from a, rotating-anode source. A total of 35 936 observations were processed with, XENGEN1.3 and scaled to yield 16 255 unique reflections with R(symm)(I) of, 4.1%. The crystals are triclinic, with unit-cell dimensions a = 29.89, b =, 53.42, c = 25.35 A, alpha = 93.67, beta = 96.88, gamma = 89.24 degrees, space group P1, with one molecule in the unit cell. The atomic coordinates, of the wild-type Paramecium calmodulin (PCaM) studied in our laboratory, provided the starting model. Refinement of the structure by X-PLOR and, refitting it into omit maps yielded an R value of 0.194 for 15 965, reflections greater than 3sigma(F) in the 6.0-1.68 A resolution range. The, final model contained 1165 protein atoms for all of the 148 residues, four, Ca(2+) ions, and 172 water molecules. The dumbbell structure has seven, alpha-helices including a long 7.8 turn central helix connecting the two, terminal domains each containing two EF-hand (helix-loop-helix motif), calcium-binding sites. The loops within each pair of EF-hand motifs in the, N- and C-terminal domains are brought into juxtaposition to form a pair of, hydrogen-bonded antiparallel beta-sheets which are extended at either ends, by water bridges. The four calcium-binding EF-hands are superposable with, r.m.s. deviations of 0.31-0.79 A. The best agreement is between site 1 and, site 3 and the worst agreement is between site 1 and 4. The largest, differences are in the ninth and tenth residues of the calcium-binding, loops probably because of their involvement in the mini beta-sheets. The, calcium coordination distances vary between 2.04 and 2.69 A, average 2.34, A. The rPCaM and wild-type PCaM have an r.m.s. deviation of 0.36 A for, equivalent C(alpha) atoms. The side chains of Lys13 and Lys115 are more, extended in rPCaM compared to the wild type where the post-translational, modified di- and tri-methylated lysine residues are more folded. The, sequence of PCaM differs from those of mammalian (MCaM) and Drosophila, calmodulin (DCaM), but the overall structures are very similar, with, r.m.s,. deviations of 0.44 and 1.68 A for equivalent C(alpha) atoms, respectively. However, in rPCaM, the first four N-terminal residues, stretch out and make intermolecular crystal contacts, in contrast to those, in recombinant Drosophila calmodulin (rDCaM), they stretch out in the, opposite direction and towards the second calcium-binding site (see note, below), while in MCaM and wild-type PCaM, the N-terminal residues are not, visible. The central helix in rPCaM has all its backbone hydrogen bonds, intact with no unusually long separation between the carbonyl and amide, groups as found in MCaM and rDCaM.
About this Structure
1OSA is a Single protein structure of sequence from Paramecium tetraurelia with CA as ligand. Full crystallographic information is available from OCA.
Reference
Structure of the recombinant Paramecium tetraurelia calmodulin at 1.68 A resolution., Ban C, Ramakrishnan B, Ling KY, Kung C, Sundaralingam M, Acta Crystallogr D Biol Crystallogr. 1994 Jan 1;50(Pt 1):50-63. PMID:15299476
Page seeded by OCA on Tue Nov 20 23:09:11 2007
