The calpain system originally comprised three molecules: two Ca2+-dependent proteases, mu-calpain and m-calpain, and a third polypeptide, calpastatin, whose only known function is to inhibit the two calpains. Both mu- and m-calpain are heterodimers containing an identical 28-kDa subunit and an 80-kDa subunit that shares 55-65% sequence homology between the two proteases. The crystallographic structure of m-calpain reveals six "domains" in the 80-kDa subunit: 1). a 19-amino acid NH2-terminal sequence; 2). and 3). two domains that constitute the active site, IIa and IIb; 4). domain III; 5). an 18-amino acid extended sequence linking domain III to domain IV; and 6). domain IV, which resembles the penta EF-hand family of polypeptides. The single calpastatin gene can produce eight or more calpastatin polypeptides ranging from 17 to 85 kDa by use of different promoters and alternative splicing events. The physiological significance of these different calpastatins is unclear, although all bind to three different places on the calpain molecule; binding to at least two of the sites is Ca2+ dependent. Since 1989, cDNA cloning has identified 12 additional mRNAs in mammals that encode polypeptides homologous to domains IIa and IIb of the 80-kDa subunit of mu- and m-calpain, and calpain-like mRNAs have been identified in other organisms. The molecules encoded by these mRNAs have not been isolated, so little is known about their properties. How calpain activity is regulated in cells is still unclear, but the calpains ostensibly participate in a variety of cellular processes including remodeling of cytoskeletal/membrane attachments, different signal transduction pathways, and apoptosis. Deregulated calpain activity following loss of Ca2+ homeostasis results in tissue damage in response to events such as myocardial infarcts, stroke, and brain trauma.

The Calpain System

Endothelins are a newly described peptide family consisting of three peptides (ET-1, ET-2 and ET-3) which are the most potent vasoconstrictive peptides known. They are crucial in the regulation of vascular smooth muscle tone. The diverse functions of endothelins are thought to be mediated by interaction with many different receptors coupled to the inositol phosphate/calcium ion messenger pathway. However, because of the structural resemblance of the three peptides, the presence and nature of multiple endothelin receptors remain to be elucidated. We report here the cloning of a complementary DNA encoding a bovine endothelin receptor, which has a transmembrane topology similar to that of other G protein-coupled receptors and shows specific binding, with the highest selectivity to ET-1 in animal cells transfected with the cloned cDNA. This receptor messenger RNA is widely distributed in the central nervous system and peripheral tissues, particularly in the heart and lung. Our results support the view that there are other receptor subtypes.

Cloning and expression of a cDNA encoding an endothelin receptor

A complementary DNA encoding the rat NMDA receptor has been cloned and characterized. The single protein encoded by the cDNA forms a receptor-channel complex that has electrophysiological and pharmacological properties characteristic of the NMDA receptor. This protein has a significant sequence similarity to the AMPA/kainate receptors and contains four putative transmembrane segments following a large extracellular domain. The NMDA receptor messenger RNA is expressed in neuronal cells throughout the brain regions, particularly in the hippocampus, cerebral cortex and cerebellum.

Molecular cloning and characterization of the rat NMDA receptor

Protein Kinase C: Structure, Function, and Regulation

https://www.cell.com/cell/pdf/0092-8674(92)90167-B.pdf

The SH2 and SH3 domain-containing protein GRB2 links receptor tyrosine kinases to ras signaling

Studies on the phosphorylation of myelin basic protein by protein kinase C and adenosine 3':5'-monophosphate-dependent protein kinase.

Activation of cellular protein kinase C and mode of inhibitory action of phospholipid-interacting compounds.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2886%2980060-6

A calcium-protease activator associated with brain microsomal-insoluble elements

Small amounts (0.1-0.5 mM) of deoxycholate enhanced amylase secretion, which had been induced by submaximal doses of carbachol or cholecystokinin octapeptide, without affecting the maximal levels of these reactions from isolated rat pancreatic acini. Deoxycholate alone did not induce these reactions. The other bile acids such as cholate, chenodeoxycholate, ursodeoxycholate, and taurocholate were also active. Under the similar conditions, deoxycholate enhanced the secretagogue-induced diacylglycerol formation that was derived mainly from the phospholipase C-mediated hydrolysis of phosphatidylinositol and phosphatidylinositol-4-monophosphate. Deoxycholate did not enhance the secretagogue-induced hydrolysis of phosphatidylinositol-4,5-bisphosphate or Ca2+ mobilization. Deoxycholate did not affect amylase secretion, which was induced by the simultaneous addition of protein kinase C-activating 12-O-tetradecanoylphorbol-13-acetate and Ca2+ ionophore ionomycin. Since diacylglycerol and Ca2+ may be responsible for the secretagogue-induced amylase secretion, our results indicate that small amounts of bile acids increase the sensitivity to the secretagogue of diacylglycerol formation and subsequent activation of protein kinase C, and thereby enhance amylase secretion from pancreatic acini.

/pdf/enhancement-of-secretagogue-induced-phosphoinositide-3u82ui4w2u.pdf

Y Takeyama

Papers

Studies on the phosphorylation of myelin basic protein by protein kinase C and adenosine 3':5'-monophosphate-dependent protein kinase.

Activation of cellular protein kinase C and mode of inhibitory action of phospholipid-interacting compounds.

A calcium-protease activator associated with brain microsomal-insoluble elements

Enhancement of secretagogue-induced phosphoinositide turnover and amylase secretion by bile acids in isolated rat pancreatic acini.

Presence of human immunoglobulin G anti serum pancreatic elastase 1 autoantibodies and their influence on elastase 1 radioimmunoassay