Characterization of the two size forms of the alpha 1 subunit of skeletal muscle L-type calcium channels.

Abstract

The molecular properties of two size forms of the al subunit of purified skeletal muscle calcium channels were analyzed. The minor, full-length, form, a1212, was found to have an apparent molecular mass of 214 kDa by Ferguson plot analysis, while the major, truncated, form, now designated al1o, had an apparent molecular mass of 193 kDa. Antibody mapping of the C-terminal region of allg0 with 10 anti-peptide antibodies placed the C terminus between residues 1685 and 1699. Three consensus sites for cAMP-dependent protein phosphorylation are present in the C-terminal region of a1212 but not in al1g, and they may be important for the regulation of the ion conductance activity of the calcium channel.

Phosphorylation of the L‐type calcium channel β subunit is involved in β‐adrenergic signal transduction in canine myocardium

“…But, in contrast to the latter authors we did not detect the phosphorylated 250 kDa full-length form of the ~1, subunit. The most likely explanation for this result is the low abundance of the untruncated 01, form which has been reported not to exceed 10% of the total amount of DHP receptors [40]. Although the data do not exclude the possibility that the full-length form of the cardiac dir protein serves as a substrate of PKA, a physiological role of its phosphorylation is questionable.…”

Tissue-specific expression of calcium channels

“…The product of the CaChl gene occurs in skeletal muscle in two isoforms: a minor form (-5%) of 212 kD containing the complete amino acid sequence encoded by a, mRNA, and a major form (-95%) of 190 kD that is derived from the fulllength product by posttranslational proteolysis close to amino acid residue 1690 (De Jongh et al 1991). Presumably, the shorter form is involved functionally at the triad in excitationcontraction coupling of the skeletal muscle.…”

Sites of proteolytic processing and noncovalent association of the distal C-terminal domain of CaV1.1 channels in skeletal muscle

“…Rabbit polyclonal anti-CP1 and anti-CP11 antibodies were generated against peptides corresponding to residues (1857-1873) and (1601-1618) of the rabbit skeletal muscle ␣ 1 sequence (21) and characterized as described (14). Monoclonal anti-myc antibody was purchased from Invitrogen.…”

“…The predominant (Ͼ90%) short form results from in vivo proteolytic processing of the C terminus near amino acid residue 1685, approximately halfway through the C-terminal domain (14). Similarly, the related Ca V 1.2 channels in heart and brain are also truncated by in vivo proteolysis at a similar position in their C termini (17)(18)(19)(20).…”

“…Two size forms of the ␣ 1 -subunit of Ca V 1.1 channels, Ϸ175 and 212 kDa, exist in membrane preparations from skeletal muscle (13)(14)(15)(16). The predominant (Ͼ90%) short form results from in vivo proteolytic processing of the C terminus near amino acid residue 1685, approximately halfway through the C-terminal domain (14).…”