The N terminus of the cardiac L-type Ca(2+) channel alpha(1C) subunit. The initial segment is ubiquitous and crucial for protein kinase C modulation, but is not directly phosphorylated

• Published in: The Journal of biological chemistry Vol. 274; no. 44; pp. 31145 - 31149
• Main Authors: Shistik, E, Keren-Raifman, T, Idelson, G H, Blumenstein, Y, Dascal, N, Ivanina, T
• Format: Journal Article
• Language: English
• Published: United States 29.10.1999
• Subjects: Amino Acid Sequence; Animals; Brain Chemistry; Calcium Channels, L-Type - isolation & purification; Calcium Channels, L-Type - metabolism; Enzyme Activation; Ion Channel Gating; Molecular Sequence Data; Myocardium - chemistry; Patch-Clamp Techniques; Peptide Fragments - isolation & purification; Peptide Fragments - metabolism; Phosphorylation; Protein Isoforms - isolation & purification; Protein Isoforms - metabolism; Protein Kinase C - metabolism; Rabbits; Rats; Rats, Wistar; Recombinant Fusion Proteins - metabolism; Sequence Homology, Amino Acid
• ISSN: 0021-9258
• DOI: 10.1074/jbc.274.44.31145

The first 46 amino acids (aa) of the N terminus of the rabbit heart (RH) L-type cardiac Ca(2+) channel alpha(1C) subunit are crucial for the stimulating action of protein kinase C (PKC) and also hinder channel gating (Shistik, E., Ivanina, T., Blumenstein, Y., and Dascal, N. (1998) J. Biol. Chem. 273, 17901-17909). The mechanism of PKC action and the location of the PKC target site are not known. Moreover, uncertainties in the genomic sequence of the N-terminal region of alpha(1C) leave open the question of the presence of RH-type N terminus in L-type channels in mammalian tissues. Here, we demonstrate the presence of alpha(1C) protein containing an RH-type initial N-terminal segment in rat heart and brain by using a newly prepared polyclonal antibody. Using deletion mutants of alpha(1C) expressed in Xenopus oocytes, we further narrowed down the part of the N terminus crucial for both inhibitory gating and for PKC effect to the first 20 amino acid residues, and we identify the first 5 aa as an important determinant of PKC action and of N-terminal effect on gating. The absence of serines and threonines in the first 5 aa and the absence of phosphorylation by PKC of a glutathione S-transferase-fusion protein containing the initial segment suggest that the effect of PKC does not arise through a direct phosphorylation of this segment. We propose that PKC acts by attenuating the inhibitory action of the N terminus via phosphorylation of a remote site, in the channel or in an auxiliary protein, that interacts with the initial segment of the N terminus.