Abstract
Isoform 3f of the plasma membrane Ca(2+) pump is a major isoform of this pump in rat skeletal muscle. It has an unusual structure, with a short carboxyl-terminal regulatory region of only 33 residues when compared with the 77 to 124 residues found in the other isoforms. Also, whereas the regulatory regions of the other isoforms, downstream of the alternative splice, consist of two homologous groups, the sequence of 3f is not related to either group. A synthetic peptide representing the calmodulin binding domain of isoform 3f had a much lower calmodulin affinity (with a K(d) of 15 nM) than the corresponding peptide of isoform 2b (K(d) value was 0.2 nM). The characteristics of this domain were further studied by making chimeras of the 3f regulatory region with the catalytic core of isoform 4 and by making the full-length isoform 3f. Both constructs bound to calmodulin-Sepharose. The chimera was fully active without calmodulin, showing no stimulation of activity when calmodulin was added. The full-length isoform 3f was slightly activated by calmodulin. These data show that the regulatory region of isoform 3f is only a weak autoinhibitor of the enzyme, in contrast to the properties of all the other isoforms studied so far. Rather, this isoform is a special-purpose, constitutively active form of the enzyme, expressed primarily in skeletal muscle and as a minor isoform in brain.
Highlights
In the regulatory region of the plasma membrane Ca2ϩ pump (PMCA),1 a common pattern relates all of the major isoforms: the regulatory regions are at the carboxyl terminus of the molecule, preceded by over 1000 upstream residues
We show here that isoform 3f is expressed in rat skeletal muscle at a higher level than that of other PMCA isoforms
In this Western blot, three antibodies were tested for their reactivity with four isoforms of PMCA expressed in COS cells
Summary
In the regulatory region of the plasma membrane Ca2ϩ pump (PMCA),1 a common pattern relates all of the major isoforms: the regulatory regions are at the carboxyl terminus of the molecule, preceded by over 1000 upstream residues. The properties of the regulatory region of isoform 3f were tested by studying the affinity for calmodulin of a peptide representing the 28-residue calmodulin binding region of rPMCA3f.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call