Abstract
TRAPPC11 has been implicated in membrane traffic and lipid-linked oligosaccharide synthesis, and mutations in TRAPPC11 result in neuromuscular and developmental phenotypes. Here, we show that TRAPPC11 has a role upstream of autophagosome formation during macroautophagy. Upon TRAPPC11 depletion, LC3-positive membranes accumulate prior to, and fail to be cleared during, starvation. A proximity biotinylation assay identified ATG2B and its binding partner WIPI4/WDR45 as TRAPPC11 interactors. TRAPPC11 depletion phenocopies that of ATG2 and WIPI4 and recruitment of both proteins to membranes is defective upon reduction of TRAPPC11. We find that a portion of TRAPPC11 and other TRAPP III proteins localize to isolation membranes. Fibroblasts from a patient with TRAPPC11 mutations failed to recruit ATG2B-WIPI4, suggesting that this interaction is physiologically relevant. Since ATG2B-WIPI4 is required for isolation membrane expansion, our study suggests that TRAPPC11 plays a role in this process. We propose a model whereby the TRAPP III complex participates in the formation and expansion of the isolation membrane at several steps.