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Calmodulin, S-100, and crayfish sarcoplasmic calcium-binding protein crystals suitable for X-ray diffraction studies.

1980; Elsevier BV; Volume: 255; Issue: 17 Linguagem: Inglês

10.1016/s0021-9258(19)70622-x

1083-351X

Robert H. Kretsinger, Suzanne E. Rudnick, D. Sneden, Virginia B. Schatz,

Computational Drug Discovery Methods

We have grown crystals of calmodulin, of 5-100, and of crayfish sarcoplasmic calcium-binding protein and are now determining their structures by x-ray diffraction.The sarcoplasmic calcium-binding protein crystallizes from 50% 2-methyl-2,4-pentanediol in space group P212121 with unit cell dimensions of 58.9, 68.5, and 116.1 A, and diffracts beyond 3.0 A Bragg spacing.S-100 crystallizes from 15% polyethylene glycol 6000 in space grou P41 with unit cell dimensions of 56.0, 56.0, and 112.8 x, and diffracts beyond 3.0 A. Calmodulin crystallizes from 15% polyethylene glycol in space grou P21 with unit cell dimensions of 61.8, 56.7, and 40.0 x, / 3 = 92.7",and diffracts beyond 5.0 A.Calcium-modulated proteins are defined by their presence in the cell cytosol or on the surface of a membrane facing the cytosol.Here they bind calcium with moderately high affinity, pK,, (Ca'+) 5 to 7 .Many of these proteins, e.g.calmodulin, the calcium-binding component of troponin, myosin light chains, parvalbumin, intestinal calcium-binding protein, and S-100, are homologous to one another (review by Kretsinger, 1980).The crystal structure of parvalbumin (Moews and Kretsinger, 1975) contains three homolog domains, called EF-hands.Each EF-hand domain contains a 10-to 12-residue a helix, a calcium-binding loop, followed by a second a helix region.The amino acid sequences of these other calcium-modulated proteins indicate that each contains from one to four such homolog domains.Kretsinger and Barry (1975) predicted that the four domains of troponin C, and, by inference, of calmodulin and of the myosin light chains, are arranged in two pairs with approximate point group symmetry 222 for the entire monomer.The S-100 group of proteins is found primarily in glial cells and represents up to 0.2% of the total soluble brain protein.The two predominant components of this group are called PAP I-a and PAP I-b (phenylalanine-rich protein) (Isobe et al., 1977).We have worked with PAP I-b, which we call here S-100b, because its amino acid sequence has been determined (Isobe et al., 1978; Isobe and Okuyama, 1978).The exact biological function of S-100 remains unknown.However, studies on rat brain S-100 levels during development suggest that it is related to the maturation and, possibly, differentiation of glial cells (Labourdette and Mandel, 1978).Other workers implicate S-100 in the control of membrane