Membrane Curvature Promotes ER-PM Contact Formation via Junctophilin-EHD Interactions

Area of Science:

• Cell biology
• Membrane biophysics
• Cardiovascular research

Background:

• Endoplasmic reticulum-plasma membrane (ER-PM) contact sites are vital for calcium and lipid homeostasis.
• The spatial regulation of ER-PM contacts on the plasma membrane remains poorly understood.
• ER-PM contacts in cardiomyocytes are enriched at transverse tubules (T-tubules), suggesting a role for membrane geometry.

Purpose of the Study:

• To investigate the role of plasma membrane curvature in the formation of ER-PM contacts.
• To identify the molecular mechanisms and proteins involved in curvature-dependent ER-PM tethering in cardiomyocytes.

Main Methods:

• Controlled manipulation of plasma membrane invaginations to alter local curvature.
• Analysis of ER-PM contact formation in response to induced membrane curvature.
• Biochemical assays to study protein-protein interactions, including junctophilin and EHD proteins.
• Investigating the role of junctophilin domains (LCR, MORN motifs) in membrane binding and curvature targeting.

Main Results:

• Plasma membrane curvature was shown to locally induce ER-PM contact formation in cardiomyocytes.
• Junctophilins, but not extended synaptotagmin 2, preferentially target curved plasma membrane regions.
• Both LCR and MORN motifs of junctophilins are required for targeting curved membranes.
• Eps15-homology domain containing proteins (EHDs) interact with junctophilins and mediate their preferential tethering to curved PM.

Conclusions:

• Plasma membrane curvature is a critical determinant for the spatial organization of ER-PM contact sites in cardiomyocytes.
• Junctophilins, in conjunction with EHD proteins, provide a novel mechanism for sensing and responding to membrane curvature.
• This study reveals a new paradigm for regulating organelle contact site positioning based on membrane geometry.