Abstract

Sarcoplasmic reticulum Ca2+-ATPase (SERCA) and phospholamban (PLB) are essential components of the cardiac Ca2+ transport machinery. PLB phosphorylation at residue Ser16 (pSer16) enhances SERCA activity in the heart via an unknown structural mechanism. Here, we report a fully atomistic model of SERCA bound to phosphorylated PLB and study its structural dynamics on the microsecond time scale using all-atom molecular dynamics simulations in an explicit lipid bilayer and water environment. The unstructured N-terminal phosphorylation domain of PLB samples different orientations and covers a broad area of the cytosolic domain of SERCA but forms a stable complex mediated by pSer16 interactions with a binding site formed by SERCA residues Arg324/Lys328. PLB phosphorylation does not affect the interaction between the transmembrane regions of the two proteins; however, pSer16 stabilizes a disordered structure of the N-terminal phosphorylation domain that releases key inhibitory contacts between SERCA and PLB. We found that PLB phosphorylation is sufficient to guide the structural transitions of the cytosolic headpiece that are required to produce a competent structure of SERCA. We conclude that PLB phosphorylation serves as an allosteric molecular switch that releases inhibitory contacts and strings together the catalytic elements required for SERCA activation. This atomistic model represents a vivid atomic-resolution visualization of SERCA bound to phosphorylated PLB and provides previously inaccessible insights into the structural mechanism by which PLB phosphorylation releases SERCA inhibition in the heart.

Highlights

  • The sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA) is a critical molecular component of cardiac muscle cells, regulating the rate of cardiac muscle relaxation and restoring the SR Ca2+ load necessary for muscle contraction in subsequent beats [1]

  • Complementary root mean square deviation (RMSD) plots showed that the TM helix rapidly settles a plateau around 1 Å in all eight trajectories, indicating that the TM domain converged to a position that is essentially identical to that of the initial structure used in this study (Figure 1b)

  • We present an atomistic structure of phosphorylated PLB bound to SERCA and its structural dWyneapmriecsseunntdaernCaat2o+-mfreisetciconsdtrituiocntus,rtehuosf pprhoovsidpihnogrnyelwatiendsiPghLtBs ibntooutnhde mtoecShEaRniCsmAfoarnrdegituslasttirounctural dynaomf SicEsRuCnAdbeyr CPLaB2+p-fhroesepchoonrydliattiioonns.,ItnhaugsrpeermoveindtiwngithneEwPRinasnidghNtsMinRtosptehcetrmosecochpyansitsumdiefsor[9r,e1g5u],lation of SEMRDCsAimbuylaPtiLonBspshhoowspedhothraytlathtieoNn.-teInrmaignrael edmomenaitnwofitphhEosPpRhoarnydlatNedMPRLBspiselcatrrgoeslycoupnystrsutuctduireesd[9,15], molecular dynamics (MD) isnimthuelactoiomnpslsehx,owbuetdithfaotrmthse aN-sttearbmleinhaeltedrodmimaienriocf cpohmopsplehxowryiltahteSdERPCLAB isinlatrhgeelmy iucrnosstercuocntdured in the ctoimmepsclaelxe,. bTuhet iint tfeorramctisoan sotfatbheledhiseotredreordedimNe-rtiecrmcoinmalpplehxoswphitohrySlEatRioCnAdoimn athineomf PicLrBowseicthonSdERtCimAescale

Read more

Summary

Introduction

The sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA) is a critical molecular component of cardiac muscle cells, regulating the rate of cardiac muscle relaxation and restoring the SR Ca2+ load necessary for muscle contraction in subsequent beats [1]. SERCA activity is regulated in the heart by phospholamban (PLB), a 52-residue membrane protein that resides in the SR [3]. PLB inhibits SERCA activity by decreasing Ca2+ affinity, and inhibition is relieved by phosphorylation, thereby regulating SERCA activity and muscle contractility [4]. PLB phosphorylation at residue Ser (pSer16) induces an order-to-disorder structural transition of the cytosolic domain of PLB, destabilizing a inhibitory ordered T state in favor of the disordered, non-inhibitory R state [5,6]. Two mechanisms have been proposed for the relief of SERCA inhibition by PLB phosphorylation: dissociation model and subunit model. The dissociation model proposes that upon the formation of the R state, PLB physically separates from SERCA to relieve inhibition [7,8] whereas the subunit model hypothesizes that PLB acts as a functional subunit of SERCA, and that the

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call