Conserved luminal C-terminal domain dynamically controls interdomain communication in sarcolipin

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Sarcolipin (SLN) mediates Ca<jats:sup>2+</jats:sup> transport and metabolism in muscle by regulating the activity of the Ca<jats:sup>2+</jats:sup> pump SERCA. SLN has a conserved luminal C-terminal domain that contributes to the its functional divergence among homologous SERCA regulators, but the precise mechanistic role of this domain remains poorly understood. We used all-atom molecular dynamics (MD) simulations of SLN totaling 77.5 μs to show that the N- (NT) and C-terminal (CT) domains function in concert. Analysis of the MD simulations showed that serial deletions of SLN C-terminus does not affect the stability of the peptide nor induce dissociation of SLN from the membrane but promotes a gradual decrease in both tilt angle of the transmembrane helix and the local thickness of the lipid bilayer. Mutual information analysis showed that the NT and CT domains communicate with each other in SLN, and that interdomain communication is partially or completely abolished upon deletion of the conserved segment Tyr29-Tyr31 as well as by serial deletions beyond this domain. Phosphorylation of SLN at residue Thr5 also induces changes in the communication between the CT and NT domains, thus providing additional evidence for interdomain communication within SLN. We found that interdomain communication is independent of the force field used and lipid composition, thus demonstrating that communication between the NT and CT domains is an intrinsic functional feature of SLN. We propose the novel hypothesis that the conserved C-terminus is an essential element required for dynamic control of SLN regulatory function.</jats:p><jats:sec><jats:title>Abstract Figure</jats:title><jats:fig id="ufig1" position="float" fig-type="figure" orientation="portrait"><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="013425v2_ufig1" position="float" orientation="portrait" /></jats:fig></jats:sec>

Dwarf open reading frame (DWORF) peptide is a direct activator of the sarcoplasmic reticulum calcium pump SERCA

“…Both starting models quickly converged on a helixlinker-helix structure, though the overall structure was dynamic in the simulations and varied somewhat depending on the starting model. A similar behavior has been observed with SLN (15). We consider the second model, the helix-linker-helix model with an unwound region centered on Pro 15 , to be the more stable and probable structure of DWORF ( Figure 2B).…”

“…A similar behavior has been observed with SLN (15). We consider the second model, the helix-linker-helix model with an unwound region centered on Pro 15 , to be the more stable and probable structure of DWORF ( Figure 2B). This model was maintained over 2000 ns of MD simulations, though again the structure was dynamic on its own in a lipid bilayer (Figure 2A).…”

“…The helical transmembrane domains of PLN and SLN facilitate the structural interactions in the SERCAbound states and it is a critical feature of these peptides. In contrast, the DWORF transmembrane domain appears to be discontinuous (residues Leu 17 to Ser 35 ), with a break at Pro 15 and an Nterminal helix that lies along the membrane surface (residues Met 1 to Leu 13 ).…”