title: Regulation of the sarcoplasmic reticulum calcium pump by divergent phospholamban isoforms in zebrafish.
abstract: The sarcoplasmic reticulum calcium pump (SERCA) is regulated by the small integral membrane proteins phospholamban (PLN) and sarcolipin (SLN). These regulators have homologous transmembrane regions, yet they differ in their cytoplasmic and luminal domains. Although the sequences of PLN and SLN are practically invariant among mammals, they vary in fish. Zebrafish (zf) appear to harbor multiple PLN isoforms, one of which contains 18 sequence variations and a unique luminal extension. Characterization of this isoform (zfPLN) revealed that SERCA inhibition and reversal by phosphorylation were comparable with human PLN. To understand the sequence variations in zfPLN, chimeras were created by transferring the N terminus, linker, and C terminus of zfPLN onto human PLN. A chimera containing the N-terminal domain resulted in a mild loss of function, whereas a chimera containing the linker domain resulted in a gain of function. This latter effect was due to changes in basic residues in the linker region of PLN. Removing the unique luminal domain of zfPLN ((53)SFHGM) resulted in loss of function, whereas adding this domain to human PLN had a minimal effect on SERCA inhibition. We conclude that the luminal extension contributes to SERCA inhibition but only in the context of zfPLN. Although this domain is distinct from the SLN luminal tail, zfPLN appears to use a hybrid PLN-SLN inhibitory mechanism. Importantly, the different zebrafish PLN isoforms raise the interesting possibility that sarcoplasmic reticulum calcium handling and cardiac contractility may be regulated by the differential expression of PLN functional variants.
authors.affiliation: From the Department of Biochemistry and.
authors.forename: Przemek A
authors.initials: PA
authors.lastname: Gorski
authors.affiliation: From the Department of Biochemistry and National Institute for Nanotechnology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Catharine A
authors.initials: CA
authors.lastname: Trieber
authors.affiliation: From the Department of Biochemistry and.
authors.forename: Ghazaleh
authors.initials: G
authors.lastname: Ashrafi
authors.affiliation: From the Department of Biochemistry and National Institute for Nanotechnology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada hyoung@ualberta.ca.
authors.forename: Howard S
authors.initials: HS
authors.lastname: Young
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D016415:Sequence Alignment; D015027:Zebrafish / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000737:chemistry / Q000378:metabolism*; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D020033:Protein Isoforms; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D029961:Zebrafish Proteins; D000099211:Phospholamban
keywords: Calcium ATPase; Cardiac Muscle; Membrane Transporter Reconstitution; Phospholamban; Protein Chimera; Sarcolipin; Sarcoplasmic Reticulum (SR); Zebrafish