THE EFFECT OF N-TERMINAL ACETYLATION ON CA2-ATPASE INHIBITION BY PHOSPHOLAMBAN()

The peptide Ac-MEKVQYLTRSAIRRASTIEMPQQAR (Ac-PLB(1-25)) representing r esidues 1-25 of phospholamban (PLB) inhibited the maximal activity of the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum by about 53% , with a K-d value of 5 mu M; the equivalent non-acetylated peptide PL B(1-25) had no effect. However, it was found that the non-acetylated p eptide increased the effective K-d value for inhibition by Ac-PLB(1-25 ) consistent with competitive binding to the ATPase, with a K-d value of 8 mu M for PLB(1-25). The non-acetylated peptide must therefore be able to bind to the ATPase, but in a conformation that does not lead t o inhibition of the ATPase. The identity of the N-terminal residue is important in determining the strength of binding; replacement of the M et residue by lie led to fourfold weaker binding, again with only bind ing of the acetylated peptide leading to inhibition of ATPase activity . (C) 1996 Academic Press, Inc.