Keywords
Recoverin, Ca2+-Sensor, Myristoyl Switch, Membrane Interaction, N-terminal, C-terminal, MD Simulation
Reference
DOI: 10.1021/acscentsci.7b00210
Abstract
Recoverin, a neuronal calcium sensor in vision, utilizes a Ca2+-activated myristoyl switch for membrane association.
Using molecular dynamics simulations, the authors show spontaneous insertion of the myristoyl moiety into membranes, highlighting the critical role of N-terminal conformation and membrane charge in stabilizing functional recoverin orientations.
Findings underscore how N-terminal structural adjustments and C-terminal flexibility regulate membrane engagement, offering insight into recoverin’s dynamic control of rhodopsin kinase (RK).
Notes
1. Membrane Binding: Myristoyl Switch in Action
- Ca2+-binding to EF2 and EF3 triggers exposure of myristoyl moiety.
- MD simulations capture spontaneous insertion of the myristoyl group into phospholipid bilayer:
- Insertion within 2–9 ns, stabilizing deep among acyl chains.
- After insertion, myristoyl stays embedded throughout 1 μs simulation.
- 💡 Fancy insight: Membrane binding is not passive but involves a dynamic N-terminal driven reorientation to insert myristoyl efficiently.
2. Role of N-terminal and C-terminal Domains
N-terminal domain:
- Essential for stable membrane binding — removal causes detachment from membrane.
- Helices A and B adjust during membrane engagement:
- Helix B shifts inward, narrowing RK binding pocket.
- Length and orientation of Helix A also shift to accommodate membrane proximity.
- Structural insight: N-terminal acts as a “gatekeeper” regulating recoverin orientation and anchoring.
C-terminal domain:
- Highly dynamic, occasionally contacting membrane via basic patches.
- Transient interaction influences orientation but may block RK binding site when too engaged.
- Removing C-terminal improves membrane anchoring (less unfavorable orientation) but delays initial membrane contact.
C-terminal “tunes” membrane interaction, balancing proper orientation vs. accessibility for RK.
3. Role of Electrostatics: Lipid Composition Matters
- Negatively charged PG lipids accelerate recoverin anchoring via interactions with basic residues K5, K37 near N-terminal.
- Even transient interactions facilitate orientation and anchoring.
- C-terminal positive patch may compete for lipid interaction, sometimes leading to unfavorable “parallel” orientations that occlude RK pocket.
4. Binding Orientations: Multiple States, Functional Implications
- Favorable orientation:
- Tilted: EF2 close, EF3 farther from membrane.
- Myristoyl properly inserted, RK site accessible.
- Unfavorable orientation:
- Parallel: C-terminal binds membrane, blocking RK site.
- Myristoyl detached or misaligned.
- Ligand (RK) binding stabilizes the favorable N-terminal conformation, suggesting recoverin may pre-form complexes with RK in cytoplasm before membrane association.
5. Mechanistic Model of Recoverin Membrane Binding
- Ca2+ binding triggers myristoyl exposure.
- Recoverin orients N-terminal toward bilayer.
- Electrostatic attraction via K5, K37 promotes contact.
- Myristoyl insertion stabilized by local N-terminal adjustments (Helix A/B movement).
- C-terminal transiently samples membrane but mostly remains flexible.
- RK binding may stabilize functional N-terminal conformation.
Recoverin’s functional state is an ensemble of regulated conformations, balancing membrane anchoring and target engagement.
Take-home Messages
- Myristoyl switch enables reversible, Ca2+-controlled membrane binding.
- N-terminal domain orchestrates myristoyl insertion and stabilization of recoverin on membranes.
- C-terminal domain serves as a regulatory modulator, fine-tuning membrane association but potentially blocking RK binding site in certain orientations.
- Membrane charge composition significantly impacts binding dynamics and orientation.
- Recoverin membrane binding is multi-layered and dynamic, integrating structural rearrangements, lipid interactions, and target (RK) modulation.
📸 Figure: Myristoyl Insertion Pathway of Recoverin
