VAPB is an endoplasmic reticulum (ER)-anchored protein that serves multiple critical cellular functions through formation of membrane contact sites and protein interactions. Its primary function involves mediating ER-organelle contact sites, particularly with mitochondria and lysosomes, through interactions with FFAT motif-containing proteins 1 2. VAPB forms dynamic subdomains at ER-mitochondria contact sites (ERMCSs) that undergo rapid remodeling within seconds, allowing metabolic adaptation while maintaining stable long-term contacts 2. The protein plays a crucial role in lipid metabolism by forming complexes with ESYT1 and ESYT2 at lipid droplet-mitochondria-ER interfaces, facilitating fatty acid transfer for β-oxidation 3. Additionally, VAPB regulates cholesterol sensing by mTORC1 through ER-lysosome contacts, working with OSBP to deliver cholesterol for growth signaling activation 4. VAPB also functions as a negative regulator of STING-mediated innate immune responses, controlling type I interferon expression 5. Disease relevance includes amyotrophic lateral sclerosis (ALS), where the P56S mutation impairs contact site remodeling and enhances inappropriate immune activation 2 5. The protein's dysfunction contributes to aberrant mTORC1 signaling in Niemann-Pick type C disease 4. VAPB represents a critical hub for inter-organelle communication essential for cellular homeostasis.