Scallop Muscle Na - Ca Exchanger can be Activated by Either AMPK and PK-A Through Phosphorylation of Ser621 in CBD2

Site directed mutagenesis has shown that Ser621 in the CBD2 sub-domain of the Ca2+-regulatory domain of scallop muscle Na+ - Ca2+ exchanger (NCX-SCA) is a substrate for cAMP-PK (PK-A) in the native membrane - bound enzyme [1, 2], and under the same conditions Na+-driven 45Ca2+ uptake is stimulated [3]. Examination of the amino acid sequence of NCX-SCA (AY567834, GenBank) shows a consensus sequence for AMP-PK in CBD2 in the Ca2+-regulatory domain, with Ser621 as the target residue. The consensus sequence for cAMP-PK in CBD2 (K618RGSV) is embedded within that for AMP-PK (L616LKRGSVEDL). Exposure of native scallop muscle membranes to constitutively active AMP-PK [4] activated Na+ - Ca2+ exchange by approximately the same factor as with cAMP-PK. These results suggest that both intra- and extracellular signals may stimulate the activity of NCX-SCA through phosphorylation of the Ca2+-regulatory domain in the large cytoplasmic loop.References1. Chen, M., Zhang, Z., Boateng-Tawiah, M. -A. and Hardwicke, P. M. D. (2000). Biol. Chem., 275, 22961-229682. Ryan, C., Shaw, G. and Hardwicke, P. M. D. (2007) Ann. N. Y. Acad. Sci., 1099, 43-523. Shaw, G. A. and Hardwicke, P. M. D. (2008) “Activation of Na+-Ca2+ Exchange by Protein Kinase A in Scallop Muscle Membranes” Biophys. J., 94, 86a4. Neumann, D., Wallimann, T., Rider, M. H., Tokarska-Schlattner, Hardie, D. G., and Schlattner, U. (2007) ‘Signaling by AMP-activated Protein Kinase’ In ‘Molecular System Bioenergetics: Energy for Life.’ 1st Ed. Edited by Saks, V. pp 303 - 338 Wiley-VCH Verlag Gmbh & Co. KGaA Weinheim, ISBN: 978-3-527-31787-5