Isolation and properties of a sarcoplasmic calcium-binding protein from crayfish

Abstract

The sarcoplasmic calcium-binding protein from crayfish muscle has been purified to homogeneity. The protein has a molecular weight of 44000, as determined by sedimentation equilibrium and Sephadex chromatography. It dissociates in the presence of sodium dodecyl sulfate, 8 M urea, or, after succinylation, into two subunits of 22000 molecular weight. The protein is free of carbohydrate and phosphorus but contains 4 g-atoms of calcium/44000 at a free calcium concentration of 0.1 muM. Approximately 45% of the polypeptide backbone appears to be alpha-helical. The amino acid composition reveals a high proportion of alanine and acidic amino acids, a normal content of aromatic amino acids, and the absence of histidine. The isoelectric point, as determined by isoelectric focusing, is 5.1. The protein contains a free threonyl NH2 terminal. Two thiols react rapidly in the native protein, six in the calcium-free form. Immunochemically, there is no difference between the protein from tail, claw, and heart muscle. In these three crayfish tissues, the concentrations of calcium-binding protein, as determined by rocket immunoelectrophoresis, are markedly different: 2.73 g/kg in tail, 0.72 in claw, and 0.073 in heart muscle. A functional analogy with the parvalbumins of vertebrates can be postulated.

Complete amino acid sequence of the sarcoplasmic calcium‐binding protein (SCP‐I) from crayfish (Astacus leptodactilus)

“…The value is in agreement with the data obtained previously by gel filtration and equilibrium sedimentation [10,11]. The amino acid composition as derived from the sequence agrees also with the composition obtained from the amino acid analysis (table 1).…”

Calexcitin: A signaling protein that binds calcium and GTP, inhibits potassium channels, and enhances membrane excitability

“…2 E and F), with an affinity (K s Ϸ 400 nM) similar to that of other sarcoplasmic calcium-binding protein-like proteins (28,29,41,42). A 45 Ca overlay blot (Fig.…”

Osteonectin cDNA sequence reveals potential binding regions for calcium and hydroxyapatite and shows homologies with both a basement membrane protein (SPARC) and a serine proteinase inhibitor (ovomucoid).

“…These substitutions might suggest different orientation of some residues serving as binding ligands within the loop. However, as seen in the calciumbinding protein of muscle (24) and in bovine S-100 protein (25) (35). In this regard, Mann et al (36) Based on our analysis of the amino acid sequence, we propose a possible model for osteonectin structure (Fig.…”

“…A search of the NBRF protein data base (18) showed sequence homology between two regions of osteonectin, Asp-165 to Lys-17t0 in domain III and Asp-258 to Glu-269 in domain IV, and the central calcium-binding loop of "EF hand" structures found in bovine brain calmodulin (22,23), the calciumbinding protein of muscle (24), and both the a and 13 chains of bovine S-100 protein (25) (Fig. 3).…”