Fig. 6.

STK16 regulates SLN inhibition of SERCA. (A) Ca²⁺ uptake assays were performed in the presence or absence of cotransfection with STK16 and NF-SLN. (B) Putative phosphorylation sites in SLN were identified to be serine-4 and threonine-5 (Fig. 7). These amino acids were subjected to site-directed alanine mutagenesis to generate Ser4Ala (S4A) and Thr5Ala (T5A) mutants. Ca²⁺ uptake assays for these mutants were performed in the presence or absence of STK16. Analyses of NF-SLN mutants, S4A and T5A, in the presence or absence of STK16 cotransfection. (C) K_Ca (pCa) is the negative logarithm of the Ca²⁺ concentration required to attain the half-maximal Ca²⁺ uptake rate. (D) S4A and T5A mutants detected by M2 immunoblots. Data are mean ± SEM. ∗, P < 0.05 versus SERCA1 alone.