Deletion of NH2−and COOH-terminal sequences destroys function of the Ca2+ATPase of rabbit fast-twitch skeletal muscle sarcoplasmic reticulum

Abstract

Deletion mutants of the Ca²⁺ ATPase of rabbit fast‐twitch skeletal muscle sarcoplasmic reticulum (SERCA1a) were constructed and expressed in COS‐1 cells. The mutants were expressed at levels 7‐ to 15‐fold lower than the wild‐type and were inactive. In vitro transcription‐translation‐insertion experiments showed that deletion of transmembrane sequences M₁ and M₂, but not of M₈, M₉, M₁₀ or the NH₂⁻ terminal 30 amino acids inhibited the stable insertion of the enzyme into the membrane. Thus there was no correlation between loss of function and membrane insertion. A signal sequence for membrane insertion may exist in M₁ and M₂.