The long term goal of this research is to elucidate the molecular and biophysical mechanism by which phospholamban (PLB) inhibits the activity of the Ca pump (SERCA2a isoform) in cardiac sarcoplasmic reticulum (SR). PLB is a pentameric phosphoprotein in cardiac SR, which is composed of five identical monomers. Previously, we demonstrated the PLB monomer is responsible for binding to SERCA2a and inhibiting it. Now, we propose to localize the binding-interaction sites between the PLB monomer and SERCA2a that lead to enzyme inhibition, and determine how the molecular interaction is regulated by key allosteric modulators including Ca concentration, nucleotides, and phosphorylation. Emphasis will be placed upon identifying amino acids in the inhibitory complex that interact directly, taking advantage of our newly developed chemical cross-linking method.
In Aim 1, we will perform Cys-scanning mutagenesis of PLB to localize distinct sites along its primary structure that cross-link to endogenous Cys residues of SERCA2a. The cross-linked Cys residues of SERCA2a will be directly identified by protein purification/peptide sequencing.
In Aim 2, Lys residues of SERCA2a that cross-link to distinct sites of PLB will be localized. By use of crosslinking agents as molecular rulers and combining results from Aims 1 and 2, we will develop an accurate 3-D model of the binding-complex formed between the PLB monomer and SERCA2a.
In Aim 3, the effects of Ca concentration, nucleotides, and the inhibitor thapsigargin on cross-linking of PLB to SERCA2a will be investigated. The hypothesis tested is that PLB binds exclusively to the Ca-free form (E2) of SERCA2a, but only that E2 state that has bound ATP or ADP.
In Aim 4, we will determine how Ca relieves PLB inhibition of SERCA2a. We hypothesize that PLB binds preferentially to E2, antagonizing Ca binding to SERCA2a, and that Ca binds preferentially to El, antagonizing PLB binding to SERCA2a. The Ca-binding site of SERCA2a responsible for dissociating PLB from the pump will be identified, and the effect of PLB on the Ca-binding affinity of SERCA2a will be quantified.
In Aim 5, we will determine how phosphorylation of PLB by protein kinases relieves PLB inhibition. The hypothesis tested is that phosphorylation of PLB directly dissociates it from SERCA2a. Here we will also determine if the two phosphorylated residues of PLB, Ser 16 and Thr 17, interact directly with SERCA2a to aid in enzyme inhibition. PLB is a key regulator of myocardial contractile dynamics. By defining its molecular mechanism of action on the Ca pump, new insights on PLB regulation of the strength of the heartbeat will result, that may ultimately lead to the design of new drugs to treat heart failure.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Method to Extend Research in Time (MERIT) Award (R37)
Project #
5R37HL049428-11
Application #
6761959
Study Section
Cardiovascular and Pulmonary Research A Study Section (CVA)
Program Officer
Varghese, Jamie
Project Start
1993-01-01
Project End
2008-06-30
Budget Start
2004-07-01
Budget End
2005-06-30
Support Year
11
Fiscal Year
2004
Total Cost
$453,208
Indirect Cost
Name
Indiana University-Purdue University at Indianapolis
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
603007902
City
Indianapolis
State
IN
Country
United States
Zip Code
46202
Chan, Yi-Hsin; Tsai, Wei-Chung; Song, Zhen et al. (2015) Acute reversal of phospholamban inhibition facilitates the rhythmic whole-cell propagating calcium waves in isolated ventricular myocytes. J Mol Cell Cardiol 80:126-35
Sirenko, Syevda; Maltsev, Victor A; Maltseva, Larissa A et al. (2014) Sarcoplasmic reticulum Ca2+ cycling protein phosphorylation in a physiologic Ca2+ milieu unleashes a high-power, rhythmic Ca2+ clock in ventricular myocytes: relevance to arrhythmias and bio-pacemaker design. J Mol Cell Cardiol 66:106-15
Akin, Brandy L; Hurley, Thomas D; Chen, Zhenhui et al. (2013) The structural basis for phospholamban inhibition of the calcium pump in sarcoplasmic reticulum. J Biol Chem 288:30181-91
Akin, Brandy L; Jones, Larry R (2012) Characterizing phospholamban to sarco(endo)plasmic reticulum Ca2+-ATPase 2a (SERCA2a) protein binding interactions in human cardiac sarcoplasmic reticulum vesicles using chemical cross-linking. J Biol Chem 287:7582-93
Chen, Zhenhui; Akin, Brandy L; Jones, Larry R (2010) Ca2+ binding to site I of the cardiac Ca2+ pump is sufficient to dissociate phospholamban. J Biol Chem 285:3253-60
Akin, Brandy L; Chen, Zhenhui; Jones, Larry R (2010) Superinhibitory phospholamban mutants compete with Ca2+ for binding to SERCA2a by stabilizing a unique nucleotide-dependent conformational state. J Biol Chem 285:28540-52
Chopra, Nagesh; Yang, Tao; Asghari, Parisa et al. (2009) Ablation of triadin causes loss of cardiac Ca2+ release units, impaired excitation-contraction coupling, and cardiac arrhythmias. Proc Natl Acad Sci U S A 106:7636-41
Chen, Zhenhui; Akin, Brandy L; Jones, Larry R (2007) Mechanism of reversal of phospholamban inhibition of the cardiac Ca2+-ATPase by protein kinase A and by anti-phospholamban monoclonal antibody 2D12. J Biol Chem 282:20968-76
Chen, Zhenhui; Akin, Brandy L; Stokes, David L et al. (2006) Cross-linking of C-terminal residues of phospholamban to the Ca2+ pump of cardiac sarcoplasmic reticulum to probe spatial and functional interactions within the transmembrane domain. J Biol Chem 281:14163-72
Chen, Zhenhui; Stokes, David L; Jones, Larry R (2005) Role of leucine 31 of phospholamban in structural and functional interactions with the Ca2+ pump of cardiac sarcoplasmic reticulum. J Biol Chem 280:10530-9

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