TMEM259/MEMBRALIN is a non-canonical ER-phagy receptor that associates with MAN1B1 and VCP to eliminate viral glycoproteins

Selective autophagy of the endoplasmic reticulum (ER-phagy/reticulophagy) is essential for organelle homeostasis and host defense, yet how ER quality control (ERQC) pathways distinguish viral glycoproteins from misfolded host proteins remains poorly understood. Recent work identifies TMEM259/MEMBRALIN (transmembrane protein 259) as a selective ER-phagy receptor containing a non-canonical LC3-interacting region (LIR) motif that assembles a dedicated ER-to-lysosome-associated degradation (ERLAD) complex targeting viral class I fusion glycoproteins. TMEM259 is a multi-pass ER membrane protein with luminal domains that recruit MAN1B1 (mannosyl-oligosaccharide 1,2-α-mannosidase) and cytosolic regions that engage VCP/p97 (valosin-containing protein). This TMEM259-MAN1B1-VCP axis directs diverse viral glycoproteins, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike, Ebola virus (EBOV) glycoprotein, influenza A virus (IAV) hemagglutinin (HA), and human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein, to lysosomes in a ubiquitin-independent manner. In contrast, misfolded host glycoproteins are primarily cleared through canonical ER-associated degradation (ERAD) or alternative ERLAD pathways. Preferential recognition of densely glycosylated viral substrates suggests that MAN1B1 may function as a glycan-density sensor, enabling TMEM259 to couple ER proteostasis with intrinsic antiviral immunity. These findings expand the conceptual framework of selective autophagy and uncover a specialized ER-phagy pathway dedicated to eliminating viral glycoproteins.