Biophysical Society Conference | Tahoe 2024

Molecular Biophysics of Membranes

Poster Abstracts

4-POS Board 11 SNARE MIMICRY BY CD225 PROTEINS, INCLUDING IFITM3, UNDERLIES MEMBRANE TRAFFICKING REGULATION Kazi Rahman 1 ; Isaiah Wilt 1 ; Siddhartha Datta 1 ; Alex A. Compton 1 ; 1 National Cancer Institute, Frederick, MD, USA The CD225 superfamily consists of integral membrane proteins that regulate vesicular transport and membrane fusion events driving critical cellular functions, including glucose transport, neurotransmission, and antiviral immunity. However, how the conserved CD225 domain contributes to the diverse roles played by CD225 proteins during membrane trafficking was unknown. Here, we reveal that the CD225 domain contains a SNARE-like motif that enables interaction with cellular SNARE fusogens and modulation of SNARE complex formation. CD225 member interferon-induced transmembrane protein 3 (IFITM3) exhibits broad-spectrum antiviral activity and has been shown to accelerate the trafficking of incoming virions to lysosomes for degradation. We demonstrate that IFITM3 interacts with and regulates endosomal SNARE proteins responsible for homotypic late endosome fusion. Specifically, IFITM3 binds to Q-SNARE syntaxin 7 in cells and in vitro, and this interaction requires key residues residing within a SNARE-like motif in IFITM3. Mutations in IFITM3 that abrogate syntaxin 7 binding exhibited a loss of antiviral activity against Influenza A virus. IFITM3 deficiency in human cells resulted in a greater extent of co-immunoprecipitation between Q-SNARE syntaxin 7/8 and R SNARE VAMP8, while IFITM3 overexpression inhibited this interaction. Structural modeling showed that IFITM3 adopts a VAMP-like fold that may permit displacement of VAMP8 from the SNARE complex controlling homotypic late endosome fusion. Our results suggest that IFITM3 selectively inhibits homotypic fusion of late endosomes, a pathway ensuring persistence and recycling of endocytic cargo (including viruses). Therefore, our findings invoke a mechanistic model whereby IFITM3 diverts incoming virus towards lysosomes by preventing homotypic late endosome fusion via a SNARE-like motif in its CD225 domain. Importantly, SNARE-binding activity and its determinants were shared among other members of the CD225 superfamily, including PRRT2 and TUSC5, suggesting that SNARE modulation plays a previously unrecognized central role in the diverse membrane trafficking functions performed by these proteins.

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