AMINO-ACID-SEQUENCE OF RABBIT FAST-TWITCH SKELETAL-MUSCLE CALSEQUESTRIN DEDUCED FROM CDNA AND PEPTIDE SEQUENCING

Partial amino acid sequence analysis of rabbit fast-twitch skeletal muscle calsequestrin permitted the construction of synthetic oligonucleotides that were used as both primers and probes for the synthesis and isolation of cDNAs encoding calsequestrin from neonatal rabbit skeletal muscle libraries. The cDNA sequence encodes a processed protein of 367 residues with a M(r) of 42,435 and a 28-residue amino-terminal signal sequence. The deduced amino acid sequence agreed closely with the portions of the mature protein that were sequenced using standard protein sequencing. The neonatal protein, however, contains an acidic carboxyl-terminal extension not present in the adult protein, suggesting that the cDNA sequence may have arisen from an alternatively spliced neonatal transcript. A single transcript of 1.9-2.0 kilobases was seen in neonatal skeletal muscle mRNA. A glycosylation site and two potential phosphorylation sites were detected. Although the protein contains about two acidic residues for each Ca2+ bound, there is not repeating distribution of acidic residues and no evidence of EF hand structures. Hydropathy plots show no transmembrane sequences, and structural analyses suggests that less than half of the protein is likely to be highly structured. This sequence defines the characteristics of a class of high-capacity, moderate-affinity, Ca2+ binding proteins.