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Two different molecular species of pig calpastatin. Structural and functional relationship between 107 kDa and 68 kDa molecules.

ABSTRACT: Calpastatin, the inhibitor protein acting specifically on calpain (EC 3.4.22.17; Ca2+-dependent cysteine proteinase), is known to be widely distributed in mammalian and avian cells. Two different molecular species of calpastatin were isolated and purified to homogeneity from pig heart muscle and from pig erythrocytes, and shown to be of 107 kDa and 68 kDa respectively on SDS/polyacrylamide-gel electrophoresis. Both calpastatins had very similar amino acid compositions when expressed as mol per cent of the residues, differed by only 0.1 pH unit in their isoelectric points, and showed immunological cross-reactivity. One molecule of the 107 kDa species could bind approx. 8 calpain molecules, whereas the 68 kDa inhibitor could bind approx. 5 calpain molecules. These findings suggest similar protein structures of the 107 kDa and 68 kDa calpastatins, each being composed of extended multidomains, with unit inhibitor domains aligned along the polypeptide chain of the molecule. The present study does not conclude, however, whether or not the 68 kDa calpastatin found in erythrocytes is a derived product from the 107 kDa species, which is present as such in heart muscle.

SUBMITTER: Takano E

PROVIDER: S-EPMC1146654 | biostudies-other | 1986 Apr

REPOSITORIES: biostudies-other

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Project description:Antibodies directed against whole bovine nasal-cartilage proteoglycan and against the hyaluronic acid-binding region and chondroitin sulphate peptides from the same molecule were used in immunodiffusion and immunoelectromigration experiments. Proteoglycans from bovine nasal and tracheal cartilage showed immunological identity, with all three antisera. Proteoglycans from pig hip articular cartilage, dog hip articular cartilage, human tarsal articular cartilage and rat chondrosarcoma reacted with all the antisera and showed immunological identity with the corresponding structures isolated from bovine nasal-cartilage proteoglycans. In contrast, proteoglycans from rabbit articular cartilage, rabbit nasal cartilage and cultured chick limb buds did not react with the antibodies directed against the hyaluronic acid-binding region, though reacting with antibodies raised against whole proteoglycan monomer and against chondroitin sulphate peptides. All the proteoglycans gave two precipitation lines with the anti-(chondroitin sulphate peptide) antibodies. Similarly, the proteoglycans reacting with the anti-(hyaluronic acid-binding region) antibodies gave two precipitation lines. The results indicate the presence of at least two populations of aggregating proteoglycan monomers in cartilage. The relative affinity of the antibodies for cartilage proteoglycans and proteoglycan substructures from various species was determined by radioimmunoassay. The affinity of the anti-(hyaluronic acid-binding region) antibodies for the proteoglycans decreased in the order bovine, dog, human and pig cartilage. Rat sternal-cartilage and rabbit articular-cartilage proteoglycans reacted weakly, whereas chick limb-bud and chick sternal-cartilage proteoglycans did not react. In contrast, the affinity of antibodies to chondroitin sulphate peptides for proteoglycans increased in the order bovine cartilage, chick limb bud and chick sternal cartilage, dog cartilage, rat chondrosarcoma, human cartilage, pig cartilage, rat sternal cartilage and rabbit cartilage.

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Two different molecular species of pig calpastatin. Structural and functional relationship between 107 kDa and 68 kDa molecules.

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