Four genes and alternative splicings at two different sites produce more than twenty isoforms of the plasma membrane calcium pump. A special type of alternative splice that involves the calmodulin binding domain of rPMCA3 produced a unique carboxyl terminus which is much shorter than the corresponding region of the other isoforms, extending only five residues beyond its calmodulin binding domain. This isoform has been called rPMCA3f. A synthetic peptide (c28R3f) representing the calmodulin binding domain of rPMCA3f had a much lower calmodulin affinity (with a Ki of 10 nM) than the corresponding peptides of the "a" and "b" forms of rPMCA3 (Ki values are 0.1 and 1 nM, respectively). The characteristics of this domain were further analyzed by making chimeras of hPMCA4 with the carboxyl terminus of rPMCA3f Although this chimera bound to calmodulin Sepharose, it was fully active without calmodulin and was not stimulated by calmodulin. These data indicate that the carboxyl terminus of rPMCA3f may not serve as an autoinhibitor of the enzyme. Subsequently, we raised a specific antibody against a peptide representing the carboxyl terminus of rPMCA3f. We will use this antibody to test the existence of this isoform at the protein level. (Supported by NIH grant GM 28835 and by the Howard Hughes Medical Institute.).
|Publication status||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology