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C K Manjunath

Publications and source records attributed to C K Manjunath.

11 recordsLinked to original sources
PubMed1987

The cardiac gap junction protein (Mr 47,000) has a tissue-specific cytoplasmic domain of Mr 17,000 at its carboxy-terminus.

The molecular weight of the heart gap junctional protein subunit was, until recently, believed to be about Mr 28,000-30,000, similar to that of other previously characterized gap junctional proteins. A larger polypeptide of about Mr 44,000-47,000, which undergoes proteolysis during isolation, has recently been proposed as the form of the heart junction protein in vivo. We show here that this entity has the same amino-terminal sequence as the previously characterized Mr 29,000-30,000 component. Thus, the cardiac junctional protein has, at its carboxy-terminus, cytoplasmic domain of Mr 17,000; this domain is absent in the liver protein. These observations provide further evidence that gap junction proteins form a highly diversified family.

Amino Acid Sequence↗
PubMed1987

Human cardiac gap junctions: isolation, ultrastructure, and protein composition.

Recent experiments from our laboratory have shown that the ultrastructure and protein composition of gap junctions isolated from rat ventricles are tissue specific, i.e., markedly different from gap junctions of liver and lens. The differences include a cytoplasmic surface component characteristic for cardiac gap junctions; this component can be visualized by two ultrastructural techniques: as a fuzzy layer in electron micrographs of thin-sectioned junctional pellets and as cytoplasmic surface particles in deep-etched freeze-fractured junctions. The component corresponds to a Mr 17,500 cytoplasmic surface domain of each of the six (Mr 47,000) rat heart gap junctional channel protein subunits that make up the gap junctional channel hexamer known as a connexon. The cytoplasmic surface component is localized at the carboxy-terminal of the subunit. Within the cytoplasmic surface component, rat cardiac gap junctions are cross-linked by disulfide linkages between subunits of the same connexon and between subunits of adjacent connexons. By contrast, the Mr 28,000 liver gap junctional subunit lacks a comparably large cytoplasmic surface component, cytoplasmic surface fuzz, cytoplasmic surface particles, and intra- and interconnexon disulfide linkages. Most of these unique characteristics of cardiac gap junctions were discovered in junctions isolated from rat ventricles. Unlike liver and lens gap junctions, cardiac gap junctions from humans, non-human primates, or other large mammals have not previously been isolated and characterized. Here we report the isolation of unproteolyzed gap junctions from the ventricle of a 24 year-old man with advanced cardiomyopathy whose heart was removed for replacement by a transplanted heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Fractionation↗
PubMed1986

Rat heart gap junctions as disulfide-bonded connexon multimers: their depolymerization and solubilization in deoxycholate.

Unproteolyzed gap junctions isolated from rat heart and liver were analyzed for the presence of inter-subunit disulfide bonds by sodium dodecylsulfate polyacrylamide gel electrophoresis. Rat cardiac junctions contained multiple disulfide bonds connecting the Mr 47,000 subunits of the same connexon and of different connexons. Inter-subunit disulfide bonds were absent in liver junctions. Unproteolyzed rat heart gap junctions were resistant to deoxycholate in their oxidized state, but dissolved readily in the detergent when the disulfide bonds were cleaved with beta-mercaptoethanol. Disulfide bonding in proteolyzed cardiac junctions was limited to pairs of Mr 29,500 subunits. These junctions were not soluble in deoxycholate even in the presence of beta-mercaptoethanol. These results show that heart and liver junctions differ in their quarternary organization.

Animals↗
PubMed1985

Proteolysis of cardiac gap junctions during their isolation from rat hearts.

Gap junctions (GJ) isolated from rat hearts in presence of the protease inhibitor phenylmethylsulfonylfluoride (PMSF) contain a Mr 44,000 to 47,000 major polypeptide and have a urea-resistant layer of fuzz on their cytoplasmic surfaces, whereas junctions isolated without PMSF are proteolyzed to a Mr 29,500 polypeptide by a serine protease and have smooth cytoplasmic surfaces (C.K. Manjunath, G.E. Goings & E. Page Am. J. Physiol. 246:H865-H875, 1984). Rat liver GJ isolated with or without PMSF contain a Mr 28,000 polypeptide and have smooth cytoplasmic surfaces. Here we examine the origin, type and inhibitor sensitivity of the heart protease; why similar proteolysis is absent during isolation of rat liver gap junctions; and whether the Mr 44,000 to 47,000 cardiac GJ polypeptide is the precursor of the Mr 29,500 subunit. We show that the Mr 44,000 to 47,000 polypeptide corresponds to the unproteolyzed connexon subunit; that proteolysis of this polypeptide occurs predominantly during exposure to high ionic strength solution (0.6 M KI) which releases serine protease from mast cell granules; that this protease is inhibitable with PMSF and (less completely) soybean trypsin inhibitor and chymostatin; and that in vivo degranulation of mast cells by injecting rats with compound 48/80 fails to prevent breakdown of cardiac GJ during isolation. The results support the concept that GJ from rat heart and liver differ in protein composition.

Animals↗
PubMed1985

Cell biology and protein composition of cardiac gap junctions.

The gap junctions that electrically couple mammalian myocardial cells have high (12,000-17,000/micron2)surface densities of channel-containing elements (connexons), undulating surfaces, and approximately hexagonally arrayed connexons disposed in small domains rotated with respect to one another. Optical diffraction combined with image processing of negatively stained isolated rabbit heart gap junctions shows six protein subunits surrounding the cell-to-cell channel and suggestive (but not conclusive) evidence for protein connections between connexons. Biochemical studies indicate that the six identical relative molecular weight (Mr) 47,000 subunits of mammalian cardiac gap junctions differ from liver gap junctions in the presence of a covalently bound Mr 17,500 cytoplasmic surface component that can be visualized electron microscopically in thin-sectioned and freeze-etched hearts. The cytoplasmic surface component is susceptible to cleavage by an alkaline serine protease released from mast cell granules by high ionic strength solutions (0.6 M KI) used to extract myofibrils during gap junction purification. Interlocking of connexons from coupled cells in the gap involves hydrogen bonding between protein subunits of the connexons.

Animals↗
PubMed1985

Differences between cytoplasmic surfaces of deep-etched heart and liver gap junctions.

We have compared the ultrastructures of the cytoplasmic surfaces (CS) of isolated, glutaraldehyde-fixed gap junctional pellets from rat ventricles and liver by rapid freezing on a liquid helium-cooled surface, freeze fracture, deep etching, and double-axis rotary replication (J. Microsc. Oxford 137: 121-123, 1984). Deep-etched unproteolyzed cardiac junctions [protein subunit relative molecular wt (Mr) 44,000-47,000], isolated with phenylmethylsulfonylfluoride (PMSF) [Am. J. Physiol. 246 (Heart Circ. Physiol. 15): H865-H875, 1984; C.K. Manjunath, G.E. Goings, and E. Page. Proteolysis of cardiac gap junctions during their isolation from rat hearts. J. Membr. Biol. In press.] had particulate CS, while proteolyzed cardiac junctions (subunit Mr 29,500) made without PMSF and liver junctions (Mr 28,000) made with or without PMSF had nonparticulate CS. Taken together with our previous findings that electron micrographs of thin-sectioned isolated unproteolyzed cardiac junctions have urea-resistant fuzzy CS coatings [Am. J. Physiol. 246 (Heart Circ. Physiol. 15): H865-H875, 1984], that proteolyzed cardiac junctions and isolated liver junctions lack this fuzzy layer, and that the CS of in situ cardiac junctions is fuzzy [J. Membr. Biol. 78: 147-155, 1984; Am. J. Physiol. 246 (Heart Circ. Physiol 15): H865-H875, 1984], and published data that in situ freeze-etched liver gap junctions are nonparticulate (Cell 30: 395-406, 1982), these new observations strongly indicate that CS components of heart and liver gap junction proteins are structurally different.

Animals↗
PubMed1984

Detergent sensitivity and splitting of isolated liver gap junctions.

Isolated rat liver gap junctions were split by two methods. In the first method, isolated gap junctions were stabilized by cross-linking their cytoplasmic surfaces with glutaraldehyde under conditions that prevented the entry of glutaraldehyde into the "gap" region. The "stabilized" junctions were then split in the junctional gap with SDS. In the second procedure, unfixed gap junctions were split by incubation in urea-containing solutions. Junctional splitting was monitored by electron microscopy of thin sectioned and freeze fractured membrane pellets. Sidedness of the split junctional membranes was defined by labeling their cytoplasmic surfaces with glutaraldehyde-activated ferritin before splitting with urea. Gap junctional splitting did not result in any loss of protein components as determined by SDS-gel electrophoresis. The glutaraldehyde cross-linking procedure was also used to determine the effects of various detergents on the protein-protein interactions in the "gap" region. Of the detergents tested, only SDS caused junctional splitting.

Animals↗
PubMed1984

Cytoplasmic surface and intramembrane components of rat heart gap junctional proteins.

Gap junctions were purified from rat hearts in the presence of absence of proteolysis inhibitors and examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and electron microscopy of thin sections. In absence of proteolysis inhibitors or in presence of ethylenediaminetetraacetic acid or leupeptin, gap junctions contained a single major protein band at relative molecular weight (Mr) 29,500 and minor bands at Mr 44,000-47,000, 17,750, and 16,500 and showed smooth cytoplasmic surfaces in electron micrographs. SDS-PAGE of junctions prepared with phenylmethylsulfonylfluoride (PMSF) showed markedly decreased intensity of the Mr 29,500 band and increased intensity of bands at Mr 44,000, 45,500, and 47,000; electron microscopy of these gap junctions showed presence of a fuzzy layer on their cytoplasmic surfaces. Urea (8 M) could not remove this fuzzy layer. In electron micrographs of rat ventricular myocytes, cytoplasmic surfaces of gap junctions were fuzzy. We conclude that rat heart gap junction protein consists of an intramembrane component (Mr 29,500) that extends into the "gap" and a cytoplasmic surface component (Mr 14,500-17,500) that corresponds to the fuzzy layer and is hydrolyzable by a serine protease.

Animals↗
PubMed1982

Isolation and protein composition of gap junctions from rabbit hearts.

We have modified a method for isolating gap-junctional membrane from mouse hearts [Kensler & Goodenough (1980) J. Cell Biol. 86, 755-764] to isolate gap junctions of comparable purity from rabbit hearts more rapidly, with better yield, and without resort to non-ionic detergents. Purification was monitored by electron microscopy of thin-sectioned membrane pellets and by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Gap junctions were obtained as vesicles whose mean surface area approximated that of junctions in intact myocardial cells. About 10-20% of the vesicles were ferritin-impermeable. Approx. 125 micrograms of membrane protein was obtained per 8 g of rabbit heart. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of purified gap junctions showed five major protein bands of mol.wts. 46 000, 44 000, 33 000, 30 000 and 28 500 that co-purified with the junctions. This protein composition was nearly identical with that published for gap junctions of mouse hearts, and differed markedly from the protein composition of gap junctions from non-excitable cells (lens and liver). The constancy of junctional protein composition between hearts of two different species and its non-identity with that from liver and lens suggest that, although gap-junctional structure in mammalian tissues seems to be remarkably similar by electron-microscopic techniques, junctional-channel protein composition actually varies from tissue to tissue and may be adapted to the permeability requirements of the tissue.

Animals↗
PubMed1981

A technique for freeze fracturing minute amounts of isolated cardiac membrane.

Electron microscopy (EM) of freeze-fractured membranes provides more information about internal membrane structure than EM of thin-sectioned or negatively stained material. However, it has heretofore been impractical to use freeze fracture routinely for analysis of highly purified membrane fractions obtainable in small (micrograms) amounts, because the technique, when conventionally applied to minute pellets, yields only one fracture of unpredictable quality; it also precludes in parallel biochemical studies by using up the entire preparation. To solve this problem, we have developed a method for freeze fracturing tiny droplets of suspended membranes containing 1-10 micrograms membrane protein, thereby allowing both multiple fractures and biochemical studies. Before fracture, the final membrane fractions can be concentrated, subjected to experimental manipulations, cross-linked, and glycerinated in a dialysis bag. The technique is illustrated on isolated gap junctions from rabbit hearts, which were chosen because their unique internal membrane structure allows unequivocal identification of membrane type based on structural criteria.

Animals↗