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PubMed1998

Binding of paratropomyosin to beta-connectin from chicken skeletal muscle.

We found that paratropomyosin bound to beta-connectin, in examining binding of paratropomyosin at the junction of A- and I-bands of sarcomeres. The turbidity of a mixture of beta-connectin and paratropomyosin was greater with more paratropomyosin added, but high concentrations of Ca2+ suppress this increase. These results suggest that paratropomyosin is released from connectin filaments at the A-I junction region by increased concentrations of calcium ions in postmortem skeletal muscles.

Animals↗
PubMed1993

A novel domain sequence of connectin localized at the I band of skeletal muscle sarcomeres: homology to neurofilament subunits.

A cDNA of 4.0 kb was cloned from a chicken embryo skeletal muscle cDNA library, using an antibody to muscle elastic protein connectin (titin), the molecular mass of which is estimated to be 3,000 kDa. Immunoelectron microscopy revealed that the antiserum raised against the product of the cDNA expressed in E. coli bound to the epitopes of the connectin filament near the N2 line of chicken breast muscle sarcomeres. The predicted amino acid sequence contains eight immunoglobulin C2 motifs and regions highly homologous with the high and medium molecular weight subunits of neurofilament. In addition, there are regions homologous with desmoplakin, calsequestrin, and calpastatin.

Amino Acid Sequence↗
PubMed1994

Characterization of connectin-like proteins of obliquely striated muscle of a polychaete (Annelida).

In obliquely striated muscle of polychaete, Neanthes sp., three kinds of connectin (titin)-like high molecular weight proteins, approximately 4000 kDa, approximately 1200 kDa and approximately 700 kDa, were detected by SDS gel electrophoresis and immunoblots using antibodies to vertebrate skeletal muscle connectin and antiserum to the protein in question. The 700 kDa protein was isolated and characterized as a beta sheet-rich filament 170 nm long and 4 nm wide. Using polyclonal antibodies to the 700 kDa protein, the binding of the immunogold to the thick filament was only demonstrated in high ionic strength relaxing solution which solubilized some myosin. This observation suggested that the 700 kDa protein was localized below the layers of myosin in the thick filament and this localization is different from that of twitchin of C elegans bodywall muscle that is on the surface of thick filament. The 4000 kDa protein was identified as a very thin filament linking the thick filament to the dense body. The very thin filaments were visualized in gelsolin-treated actin filament-free fibres. The 1200 kDa protein was located in the periphery of the dense body. A model of the elastic filament in polychaete bodywall muscle is presented.

Actin Cytoskeleton↗
PubMed1986

Circular dichroism spectra show abundance of beta-sheet structure in connectin, a muscle elastic protein.

Circular dichroism spectra of native connectin from chicken breast muscle strongly suggested the abundant presence of beta-sheet structure, as much as 70% in 0.5 M KCl and 50 mM phosphate buffer, pH 7.5. alpha-Helix was not detected. These results are in contradiction with the conclusion that native connectin from rabbit skeletal muscle consists entirely of random coil [(1984) J. Mol. Biol. 180, 331-356].

Animals↗
PubMed1983

Connectin: cell surface protein that binds both laminin and actin.

A purified cell surface receptor protein for laminin (Mr = 70,000) isolated from mouse fibrosarcoma cells binds to actin with specificity and high affinity. This binding was demonstrated both by cosedimentation of the receptor with actin and binding of the receptor to actin immobilized on nitrocellulose filters. Specificity was demonstrated by displacement of 35S-labeled receptor by unlabeled receptor. Scatchard analysis of receptor binding to actin yielded a Kd of 6 X 10(-7) M. The receptor was observed to reduce the viscosity of actin filaments. It also caused the formation of bundles of parallel filaments. This observation and the stoichiometry of binding suggest that the receptor binds along the sides of actin filaments. Based on the ability of this receptor to bind both extracellular laminin and intracellular actin, we have named this protein "connectin." Connectin may be an example of a transmembrane protein that is capable of mediating the interaction of a cell with its extracellular matrix.

Actins↗
PubMed1989

The immunological homology between two filamentous cross-linker phosphoproteins, connectin and cross-bridge region of neurofilament-H, is not affected by the phosphorylation state.

It has recently been shown that a monoclonal antibody SM 1-36-2 against connectin, an elastic filament of striated muscles, binds to the "elastic" domain of the molecule, and that the H subunit of neurofilament (NF-H), an intermediate filament of nerve cells, shares a homologous domain (Shimizu, T. et al. (1988) Biomed. Res. 9, 227-234 and Itoh, Y. et al. (1988) J. Biochem. 104, 504-508). In order to characterize (1) the intramolecular localization of the domain in the NF-H and (2) the effect of the phosphorylation state on the immunoreactivity, the homologous domain in the NF-H was analyzed by Western blotting after limited digestion with trypsin or alpha-chymotrypsin and dephosphorylation with E. coli alkaline phosphatase. It was found that (1) the epitope was located not in the core region but in the carboxyl-terminal peripheral (cross-bridge) region of NF-H and (2) the epitopes in connectin and NF-H were not affected by the phosphorylation state.

Animals↗
PubMed1984

Presence of connectin-like protein in white blood cells and platelets.

Connectin is known to be an anchoring protein of actomyosin filaments in skeletal muscle. Attempts were made to extract this protein from white blood cells and platelets in order to investigate its properties. The purified connectin-like protein obtained had a rubbery appearance and was insoluble in water and immobile on SDS gel-electrophoresis. Amino acid composition and electron microscopic features of the protein were similar to those of skeletal muscles. FITC-labeled antibody to the protein showed a positive reaction to the membrane fractions of red cells, white cells and platelets. In moving cells fluorescence was observed not only in pseudopod, but also in whole cytoplasm. No changes in the fluorescence patterns were observed with respect to moving stages or cell types. The presence of the protein beneath the cell membrane was also confirmed electron micrographically.

Amino Acids↗
PubMedDate not supplied

[Connectin from muscle cells is a collagen protein].

By X-ray analysis a collagen-like structure was observed in the muscle protein connectin . Hydration of species gives a clearer diffraction pattern, which is characteristic of the collagen-like structures. The functional role of connectin should consist in the fixation of maximum length of muscular cells.

Amino Acid Sequence↗
PubMed1993

Distribution of connectin (titin) and transverse tubules at myotendinous junctions.

The ends of muscle fibers form many longitudinal projections which are further divided into numerous processes and attach to the collagen fibrils of tendons to form myotendinous junctions (MTJs). Immunocytochemical and electron microscopic observations on pectoralis muscles of the chicken revealed the presence of an elastic filamentous protein, connectin (titin), within the terminal sarcomere on the side adjacent to the terminal Z bands, and the absence of connectin and myosin and the presence of actin at the apical sarcoplasmic region of MTJ processes between the terminal Z band and the MTJ sarcolemma. Intermediate voltage electron microscopy showed that T tubules in the terminal sarcomere were absent at the level of the A-I junction on the MTJ side in the rat vastus intermedius, and at the level of the terminal Z band or under the MTJ subsarcolemmal densities in the chicken pectoralis.

Animals↗
PubMed1978

Fine structure of the myotendinous junction of lathyritic rat muscle with special reference to connectin, a muscle elastic protein.

The fine structure of the myotendinous junction of the skeletal muscle of lathyritic rats caused by beta-aminopropionitrile was investigated. In the junction there are finger-like processes of muscle fibers, in which thin filaments were extended from the last Z lines of myofibrils and attached to the sarcolemma of the processes. By the heavy meromyosin decoration technique, these thin filaments were identified as actin filaments. In the lathyritic muscle, the thin filaments were markedly fewer in number and distributed sparsely in the sarcoplasm. The content of connectin, an elastic protein, which is localized in myofibrils and also in sarcolemma was significantly decreased in the lathyritic muscle. A possible relationship between the changes in the fine structure of the myotendinous junction and in the connectin contents is discussed.

Aminopropionitrile↗
PubMed1978

Carp connectin: amino acid composition.

An elastic protein, connectin, was prepared from carp skeletal muscle by the alkaline method with some modifications; collagen contaminations were exhaustively extracted with 1 N acetic acid and hot phenol treatment was omitted. This connectin preparation contained a considerable amount of tryptophan, but almost completely lacked hydroxyproline.

Amino Acids↗
PubMed1977

Role of connectin in the length-tension relation of skeletal and cardiac muscles.

Resting length-tension relation was studied in glycerinated preparations of frog semitendinosus and atrial muscles. The sarcomere length was measured by using either the light diffraction method or photomicrographs. When the glycerinated preparation was treated with 1 N NaOH solution and subsequently with 2% SDS solution, the resting tension decreased. In glycerinated semitendinosus muscle the resting tension decreased to below 20% of the value before treatment. However, the glycerinated atrial muscle retained more than 50% of its resting tension in spite of such biochemical treatment. The thermoelasticity of the muscle, which was represented by (formula:see text), was determined. Glycerinated semitendinosus and atrial muscles, which were treated with 0.6 M KCl, showed negative beta at all sarcomere lengths. However, when the glycerinated muscle was treated with both alkali (1 N NaOH) and SDS solution, beta at the shorter length became positive (i.e., a rubber-like property). Since connectin survived the biochemical treatment (either NaOH or SDS), it was concluded that the fraction of resting tension, which remained in spite of the biochemical treatments, might be due to the connectin.

Animals↗
PubMed1995

Detection of giant myofibrillar proteins connectin and nebulin by electrophoresis in 2% polyacrylamide slab gels strengthened with agarose.

We have established an improved method of sodium dodecyl sulfate-polyacrylamide gel electrophoresis to facilitate analysis of giant myofibrillar proteins connectin and nebulin, whose molecular masses are about 3000 and 700 kDa, respectively. This method consists of 2% polyacrylamide slab gels strengthened with agarose and a specific buffer system. Our 2% polyacrylamide slab gels are superior to usual 1.8 or 2% polyacrylamide disc gels in preparation, handling, and resolution.

Animals↗
PubMed2000

Semaphorin-1a acts in concert with the cell adhesion molecules fasciclin II and connectin to regulate axon fasciculation in Drosophila.

Semaphorins comprise a large family of phylogenetically conserved secreted and transmembrane glycoproteins, many of which have been implicated in repulsive axon guidance events. The transmembrane semaphorin Sema-1a in Drosophila is expressed on motor axons and is required for the generation of neuromuscular connectivity. Sema-1a can function as an axonal repellent and mediates motor axon defasciculation. Here, by manipulating the levels of Sema-1a and the cell adhesion molecules fasciclin II (Fas II) and connectin (Conn) on motor axons, we provide further evidence that Sema-1a mediates axonal defasciculation events by acting as an axonally localized repellent and that correct motor axon guidance results from a balance between attractive and repulsive guidance cues expressed on motor neurons.

Animals↗
PubMed1997

Neuromuscular target recognition by a homophilic interaction of connectin cell adhesion molecules in Drosophila.

Drosophila Connectin (CON) is a cell surface protein of the leucine-rich repeat family. During the formation of neuromuscular connectivity, CON is expressed on the surface of a subset of embryonic muscles and on the growth cones and axons of the motoneurons that innervate these muscles, including primarily SNa motoneurons and their synaptic targets (lateral muscles). In vitro, CON can mediate homophilic cell adhesion. In this study, we generated transgenic lines that ectopically expressed CON on all muscles. In the transformant embryos and larvae, SNa motoneurons often inappropriately innervated a neighboring non-target muscle (muscle 12) that ectopically expressed CON. Furthermore, the ectopic synapse formation was dependent on the endogenous CON expression on the SNa motoneurons. These results show that CON can function as an attractive and homophilic target recognition molecule in vivo.

Animals↗
PubMed1976

Connectin, an elastic protein from myofibrils.

The elastic protein isolated from myofibrils of chicken skeletal muscle was compared with extracellular non-collagenous reticulin prepared from chicken liver and skeletal muscle. The amino acid compositions of these proteins were similar except that their contents of Phe, Leu, Cys/2, and Hyp were different. The impregnations of the elastic protein and reticulin with silver were also different. The reticulin was not at all elastic. It also differed from reticulin in solubility and antigenicity. It is proposed to call the intracellular elastic protein connectin.

Amino Acids↗
PubMed1978

Fine structure of connectin nets in cardiac myofibrils.

A net-like structure extending through Z lines of myofibrils in frog cardiac muscle was clearly demonstrated under an electron microscope after the removal of myosin and actin. The diameter of the very thin filaments forming the nets was approximately 2 nm; this width was thinner than that of the actin filament. The net structure is ascribed to connectin, an elastic protein of muscle.

Actins↗