title: Threonine-5 at the N-terminus can modulate sarcolipin function in cardiac myocytes.
abstract: Sarcolipin (SLN) has emerged as an important regulator of the atrial sarcoplasmic reticulum (SR) Ca2+ transport. The inhibitory effect of SLN on cardiac SR Ca2+ ATPase (SERCA) pump can be relieved by beta-adrenergic stimulation, which indicates that SLN is a reversible inhibitor. However, the mechanism of this reversible regulation of SERCA pump by SLN is yet to be determined. In the current study using adult rat ventricular myocytes we provide evidence that the threonine 5 (T5) residue at the N-terminus of SLN which is conserved among various species, critically regulates the SLN function. Point mutation of T5-->alanine exerts an inhibitory effect on myocyte contractility and calcium transients similar to that of wild-type SLN, whereas mutation of T5-->glutamic acid which mimics the phosphorylation abolished the inhibitory function of SLN. Our results showed that T5 can be phosphorylated in vitro by calcium-calmodulin dependent protein kinase II (CaMKII). Blocking the CaMKII activity in WT-SLN overexpressing myocytes using autocamtide inhibitory peptide completely abolished the beta-adrenergic response. Taken together, our data suggest that T5 is the key amino acid which modulates SLN function via phosphorylation/dephosphorylation mechanisms through CaMKII pathway.
authors.affiliation: Department of Physiology and Cell Biology, 304 Hamilton Hall, 1645 Neil Ave, The Ohio State University College of Medicine and Public Health, Columbus, OH 43210, USA.
authors.forename: Poornima
authors.initials: P
authors.lastname: Bhupathy
authors.forename: Gopal J
authors.initials: GJ
authors.lastname: Babu
authors.forename: Makoto
authors.initials: M
authors.lastname: Ito
authors.forename: Muthu
authors.initials: M
authors.lastname: Periasamy
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002478:Cells, Cultured; D008297:Male; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation; D011510:Proteolipids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013329:Structure-Activity Relationship; D013912:Threonine / Q000737:chemistry*
chemical_list: D009124:Muscle Proteins; D011510:Proteolipids; C077258:sarcolipin; D013912:Threonine; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium