Autoinhibitory domains of various Ca2+ transporters cross-react

Synthetic peptides having the sequence of the calmodulin-binding autoinhibitory domain of the Na+/Ca2+ exchanger (XIP) and of the plasma membrane Ca2+ pump (C28R2) inhibited the sarcoplasmic reticulum (SERCA) and plasma membrane (PMCA) Ca2+ pumps. XIP was nearly as effective in inhibiting both systems as C28R2, which had previously been considered to be the most powerful peptide inhibitor of PMCA. In contrast, calmodulin-binding peptides from non-Ca2+ transport proteins (calmodulin-dependent protein kinase II and myosin light chain kinase) showed only weak inhibition. The relative specificity and effectiveness of the peptides from the Ca2+ transport proteins, as well as the characteristics of their actions were similar in both SERCA and PMCA, suggesting a high degree of functional relatedness between these autoinhibitory regions. Secondary structure predictions show that the calmodulin-binding autoinhibitory domains of the Na+/Ca2+ exchanger and PMCA are predicted to form a beta structure which might be necessary for the observed cross-inhibition. The results also indicate that other domains of the Ca2+ transporters have common structural elements which interact with the autoinhibitory domains.