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Thesis Sana updated 4-20-15.pdf (8.72 MB)

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Regulation of the Sarco-endoplasmic Reticulum Calcium ATPase by Sarcolipin

Shaikh, Sana Ashfaque
http://orcid.org/0000-0003-2864-162X
http://rave.ohiolink.edu/etdc/view?acc_num=osu1429539826

Abstract Details

2015, Doctor of Philosophy, Ohio State University, Biochemistry Program, Ohio State.
The Sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) is crucial for intracellular Ca2+ homeostasis in muscle and non-muscle cells. SERCA activity in cardiac and skeletal muscle, is regulated by two proteins: phospholamban (PLB) and Sarcolipin (SLN). While Phospholamban (PLB) is an affinity modulator of SERCA and inhibits the pump only at low Ca2+ concentration, the role of Sarcolipin (SLN) is poorly understood. Recent data suggest that SLN could play a role in muscle thermogenesis by promoting uncoupling of the SERCA pump, but the mechanistic details are unknown. To understand how binding of SLN to SERCA promotes uncoupling of SERCA, we compared the interaction of SLN and SERCA1 with that of PLB. We used protein cross-linking to detect dynamic protein interaction as well as SERCA functional assays to observe the effects of SLN and PLB on SERCA. Our studies revealed that SLN and PLB differ significantly in their regulation of SERCA. We found that 1) SLN primarily affects the Vmax of SERCA-mediated Ca2+ uptake but not the pump affinity for Ca2+, 2) SLN does not affect the ATP hydrolysis activity of SERCA, 3) SLN can bind to SERCA in the presence of high Ca2+, and 4) SLN interacts with SERCA throughout the kinetic cycle and promotes uncoupling of the SERCA pump, unlike PLB that only interacts with the ATP-bound Ca2+-free E2 state. Using SERCA transmembrane mutants, we additionally showed that PLB and SLN bind to the same groove but interact with a different set of residues on SERCA. These data collectively suggest that the ability of SLN to interact with SERCA in the presence of Ca2+ causes uncoupling of the SERCA pump. Next, in order to determine the structural regions of SLN that mediate the uncoupling of SERCA, we employed mutagenesis and generated chimeras of PLB and SLN. We showed that SLN N-terminus deletion lead to loss of its uncoupling function although the truncated peptide constitutively bound to SERCA. Further, alanine mutagenesis of the SLN N-terminus altered its ability to interact with SERCA. MD simulations of the SLN and SERCA interaction showed that SLN N-terminus deletion introduces structural rearrangement in SERCA residues. Collectively, these studies demonstrated that the SLN N-terminus is essential for uncoupling SERCA. Interestingly, we found that transfer of the PLB cytosolic domain to SLN transmembrane (TM) and luminal tail caused loss of SLN-like function. On the other hand, swapping the PLB N-terminus with the SLN N-terminus, lead to gain of SLN-like function. These results suggest that SLN and PLB domains can be interchanged without losing the ability to regulate SERCA activity; however the resulting chimera acquires a function different from the parent molecule. Importantly, our studies highlight that the N-terminus of SLN and PLB dictates their unique function.
Muthu Periasamy, PhD (Advisor)
Charles Bell, PhD (Committee Member)
Jonathan Davis, PhD (Committee Member)
Thomas Magliery, PhD (Committee Member)
138 p.
Biochemistry; Physiology
SERCA; Sarcolipin; Phospholamban; Calcium Transport; Membrane Proteins; Protein Interaction

Recommended Citations

Citations

  • Shaikh, S. A. (2015). Regulation of the Sarco-endoplasmic Reticulum Calcium ATPase by Sarcolipin [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429539826

    APA Style (7th edition)

  • Shaikh, Sana. Regulation of the Sarco-endoplasmic Reticulum Calcium ATPase by Sarcolipin. 2015. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1429539826.

    MLA Style (8th edition)

  • Shaikh, Sana. "Regulation of the Sarco-endoplasmic Reticulum Calcium ATPase by Sarcolipin." Doctoral dissertation, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429539826

    Chicago Manual of Style (17th edition)

osu1429539826
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This open access ETD is published by The Ohio State University and OhioLINK.