Limits...
A membrane topology model for human interferon inducible transmembrane protein 1.

Weston S, Czieso S, White IJ, Smith SE, Kellam P, Marsh M - PLoS ONE (2014)

Bottom Line: Here we present data from immunofluorescence microscopy, protease cleavage, biotin-labelling and immuno-electron microscopy assays, showing that human IFITM1 has a membrane topology in which the N-terminal domain resides in the cytoplasm, and the C-terminal domain is extracellular.Furthermore, we provide evidence that this topology is conserved for all of the human interferon-induced IFITM proteins.This model is consistent with that recently proposed for murine IFITM3, but differs from that proposed for murine IFITM1.

View Article: PubMed Central - PubMed

Affiliation: MRC Laboratory for Molecular Cell Biology, University College London, London, United Kingdom.

ABSTRACT
InterFeron Inducible TransMembrane proteins 1-3 (IFITM1, IFITM2 and IFITM3) are a family of proteins capable of inhibiting the cellular entry of numerous human and animal viruses. IFITM1-3 are unique amongst the currently described viral restriction factors in their apparent ability to block viral entry. This restrictive property is dependant on the localisation of the proteins to plasma and endosomal membranes, which constitute the main portals of viral entry into cells. The topology of the IFITM proteins within cell membranes is an unresolved aspect of their biology. Here we present data from immunofluorescence microscopy, protease cleavage, biotin-labelling and immuno-electron microscopy assays, showing that human IFITM1 has a membrane topology in which the N-terminal domain resides in the cytoplasm, and the C-terminal domain is extracellular. Furthermore, we provide evidence that this topology is conserved for all of the human interferon-induced IFITM proteins. This model is consistent with that recently proposed for murine IFITM3, but differs from that proposed for murine IFITM1.

Show MeSH

Related in: MedlinePlus

IFITM membrane topology models.In Model 1, the N- and C-terminal domains are extracellular and are connected by two transmembrane domains (M1 and M2) and the conserved intracellular loop (CIL). In Model 2 the two hydrophobic domains (M1, M2) do not span the membrane, resulting in NTD, CTD and CIL domain being located in the cytoplasm. In Model 3, the NTD and CIL domain are intracellular, suggesting M1 does not span the membrane, but the CTD is located on the extracellular side of the membrane and requires that M2 spans the membrane.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4126714&req=5

pone-0104341-g001: IFITM membrane topology models.In Model 1, the N- and C-terminal domains are extracellular and are connected by two transmembrane domains (M1 and M2) and the conserved intracellular loop (CIL). In Model 2 the two hydrophobic domains (M1, M2) do not span the membrane, resulting in NTD, CTD and CIL domain being located in the cytoplasm. In Model 3, the NTD and CIL domain are intracellular, suggesting M1 does not span the membrane, but the CTD is located on the extracellular side of the membrane and requires that M2 spans the membrane.

Mentions: From their first descriptions, the IFITM proteins were thought to be membrane proteins [15]. Indeed, sequence analyses identified two hydrophobic, putative membrane interacting domains in each of the proteins. Additional studies demonstrated palmitoylation of cysteine residues adjacent to the hydrophobic domains, a post-translational modification indicative of membrane proteins [16]. However, the membrane topology of the IFITM proteins has remained ambiguous. Initially, they were suggested to be dual pass, transmembrane proteins with both N- and C-terminal domains (NTD and CTD) exposed extracellularly and a conserved intracellular loop (CIL) (Fig. 1, model 1). This model was based on the ability of antibodies against unknown IFITM1 external epitopes to aggregate leukaemia cells [15], [17], immunoprecipitation of extracellular radiolabelled IFITM1 [18] and the accessibility of IFITM3 NTD and CTD epitope tags at the cell surface by FACS and immunofluorescence assays, respectively [1].


A membrane topology model for human interferon inducible transmembrane protein 1.

Weston S, Czieso S, White IJ, Smith SE, Kellam P, Marsh M - PLoS ONE (2014)

IFITM membrane topology models.In Model 1, the N- and C-terminal domains are extracellular and are connected by two transmembrane domains (M1 and M2) and the conserved intracellular loop (CIL). In Model 2 the two hydrophobic domains (M1, M2) do not span the membrane, resulting in NTD, CTD and CIL domain being located in the cytoplasm. In Model 3, the NTD and CIL domain are intracellular, suggesting M1 does not span the membrane, but the CTD is located on the extracellular side of the membrane and requires that M2 spans the membrane.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126714&req=5

pone-0104341-g001: IFITM membrane topology models.In Model 1, the N- and C-terminal domains are extracellular and are connected by two transmembrane domains (M1 and M2) and the conserved intracellular loop (CIL). In Model 2 the two hydrophobic domains (M1, M2) do not span the membrane, resulting in NTD, CTD and CIL domain being located in the cytoplasm. In Model 3, the NTD and CIL domain are intracellular, suggesting M1 does not span the membrane, but the CTD is located on the extracellular side of the membrane and requires that M2 spans the membrane.
Mentions: From their first descriptions, the IFITM proteins were thought to be membrane proteins [15]. Indeed, sequence analyses identified two hydrophobic, putative membrane interacting domains in each of the proteins. Additional studies demonstrated palmitoylation of cysteine residues adjacent to the hydrophobic domains, a post-translational modification indicative of membrane proteins [16]. However, the membrane topology of the IFITM proteins has remained ambiguous. Initially, they were suggested to be dual pass, transmembrane proteins with both N- and C-terminal domains (NTD and CTD) exposed extracellularly and a conserved intracellular loop (CIL) (Fig. 1, model 1). This model was based on the ability of antibodies against unknown IFITM1 external epitopes to aggregate leukaemia cells [15], [17], immunoprecipitation of extracellular radiolabelled IFITM1 [18] and the accessibility of IFITM3 NTD and CTD epitope tags at the cell surface by FACS and immunofluorescence assays, respectively [1].

Bottom Line: Here we present data from immunofluorescence microscopy, protease cleavage, biotin-labelling and immuno-electron microscopy assays, showing that human IFITM1 has a membrane topology in which the N-terminal domain resides in the cytoplasm, and the C-terminal domain is extracellular.Furthermore, we provide evidence that this topology is conserved for all of the human interferon-induced IFITM proteins.This model is consistent with that recently proposed for murine IFITM3, but differs from that proposed for murine IFITM1.

View Article: PubMed Central - PubMed

Affiliation: MRC Laboratory for Molecular Cell Biology, University College London, London, United Kingdom.

ABSTRACT
InterFeron Inducible TransMembrane proteins 1-3 (IFITM1, IFITM2 and IFITM3) are a family of proteins capable of inhibiting the cellular entry of numerous human and animal viruses. IFITM1-3 are unique amongst the currently described viral restriction factors in their apparent ability to block viral entry. This restrictive property is dependant on the localisation of the proteins to plasma and endosomal membranes, which constitute the main portals of viral entry into cells. The topology of the IFITM proteins within cell membranes is an unresolved aspect of their biology. Here we present data from immunofluorescence microscopy, protease cleavage, biotin-labelling and immuno-electron microscopy assays, showing that human IFITM1 has a membrane topology in which the N-terminal domain resides in the cytoplasm, and the C-terminal domain is extracellular. Furthermore, we provide evidence that this topology is conserved for all of the human interferon-induced IFITM proteins. This model is consistent with that recently proposed for murine IFITM3, but differs from that proposed for murine IFITM1.

Show MeSH
Related in: MedlinePlus