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Updated: Feb 14, 2026

Author Spotlight: Unveiling Mitochondrial Contact Sites and Architectural Insights
Published on: June 16, 2023
GRAM domain proteins specialize functionally distinct ER-PM contact sites in human cells
Marina Besprozvannaya1, Eamonn Dickson2, Hao Li3
1Department of Molecular and Cellular Biology, University of California, Davis, Davis, United States.
Human GRAMD proteins GRAMD1a and GRAMD2a are endoplasmic reticulum-plasma membrane contact site proteins. GRAMD2a organizes specialized ER-PM contact sites involved in calcium homeostasis and STIM1 recruitment.
Area of Science:
- Cell Biology
- Membrane Biology
- Organelle Contact Sites
Background:
- Endoplasmic reticulum (ER) membrane contact sites (MCSs) are vital for cellular signaling, organelle dynamics, and homeostasis.
- Conserved yeast sterol transporters (Ltc/Lam) function at ER MCSs.
- Human GRAMD1a and GRAMD2a are homologous to yeast sterol transporters.
Purpose of the Study:
- To investigate the localization and function of human GRAMD1a and GRAMD2a at ER-MCSs.
- To determine the role of GRAMD2a in organizing ER-plasma membrane (PM) contacts and cellular functions.
Main Methods:
- Immunofluorescence microscopy to determine protein localization at ER-PM contact sites.
- Analysis of cells lacking GRAMD2a to assess its in vivo functions.
- Investigated protein co-localization with ER-PM tethers (E-Syt2/3) and PIP lipid dependence.
Main Results:
- GRAMD1a and GRAMD2a localize to distinct ER-PM MCSs.
- GRAMD2a, but not GRAMD1a, co-localizes with E-Syt2/3 tethers in a PIP lipid-dependent manner.
- GRAMD2a marks PI(4,5)P2-enriched ER-PM MCSs essential for STIM1 recruitment and influences calcium homeostasis.
Conclusions:
- Human GRAMD proteins GRAMD1a and GRAMD2a are ER-PM MCS proteins with distinct functions.
- GRAMD2a acts as an organizer of specialized ER-PM contact sites involved in calcium regulation and STIM1 recruitment.
- These findings reveal functionally specialized ER-PM domains in human cells mediated by GRAM-domain proteins.
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