Understanding Periperal Membrane Protein Interactions | BPS Thematic Meeting

Understanding Peripheral Membrane Protein Interactions: Structure, Dynamics, Function and Therapy

Thursday Speaker Abstracts

MOLECULAR DYNAMICS STUDY OF SPHINGOSINE KINASE 1 (SK1) REGULATION AT THE MEMBRANE INTERFACE Ahmed Shubbar 1 ; Mahmoud Moradi 1 ; 1 University of Arkansas, Fayetteville, AR, USA The bioactive lipid sphingosine-1-phosphate (S1P) plays a pivotal role in regulating mammalian cell growth, survival, and migration, and is essential for immune responses, vascular development, and bone homeostasis. S1P is generated by sphingosine kinases (SK1 and SK2) and subsequently released to activate G-protein-coupled receptors (S1PR1–5), influencing diverse cellular processes. Aberrant S1P accumulation is linked to cancer progression and various inflammatory and metabolic disorders. SK1 activity and plasma-membrane localization are known to be enhanced by ERK1/2-mediated phosphorylation at Ser225, yet the structural basis by which this modification alters SK1 conformation and membrane affinity remains unresolved. Ser225 lies on the regulatory loop (R-loop), distant from the catalytic site, and interacts with the N-terminal domain (NTD) through a salt-bridge network involving Asp235, His156, Arg162, and His355. It has been hypothesized that phosphorylation at Ser225 disrupts these interactions, increasing flexibility and promoting membrane recruitment required for sphingosine phosphorylation to S1P.To elucidate this mechanism, we performed triplicate microsecond-scale molecular dynamics (MD) simulations of four SK1 systems at the membrane interface: (1) apo, (2) apo with phosphorylated Ser225, (3) Mg² ⁺ ATP/Sph-bound, and (4) Mg² ⁺ ATP/Sph-bound with phosphorylated Ser225. The protein was embedded at the interface of a heterogeneous lipid bilayer composed of cholesterol, POPC, POPE, POPS, and SAPI (20:14:35:22:9 molar ratio). State-dependent differences in membrane interactions, conformational plasticity, and interdomain coupling were quantified through interface contact analysis and salt-bridge network characterization. Phosphorylation and ligand binding together modulate electrostatic interactions and stabilize distinct conformational ensembles that correlate with altered membrane affinity. These results reveal the molecular underpinnings of SK1 regulation at the lipid interface, providing mechanistic insights relevant to the design of selective allosteric modulators and inhibitors targeting this therapeutically important enzyme.

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