Stalk Domain of the Dynamin-like MxA GTPase Protein Mediates Membrane Binding and Liposome Tubulation via the Unstructured L4 Loop

• Published in: The Journal of biological chemistry Vol. 286; no. 43; pp. 37858 - 37865
• Main Authors: von der Malsburg, Alexander, Abutbul-Ionita, Inbal, Haller, Otto, Kochs, Georg, Danino, Dganit
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 28.10.2011; American Society for Biochemistry and Molecular Biology
• Subjects: Antiviral Agents; Cryoelectron Microscopy; Dynamin-like; Dynamins - chemistry; Dynamins - genetics; Dynamins - metabolism; G Proteins; GTP Hydrolysis; GTP-Binding Proteins - chemistry; GTP-Binding Proteins - genetics; GTP-Binding Proteins - metabolism; Guanosine Triphosphate - chemistry; Guanosine Triphosphate - genetics; Guanosine Triphosphate - metabolism; Humans; Hydrolysis; Innate Immunity; Interferon; Lipid-binding Protein; Membrane Lipids - chemistry; Membrane Lipids - metabolism; Membranes, Artificial; Mutation; MxA Protein; Myxovirus Resistance Proteins; Protein Multimerization; Protein Structure and Folding; Protein Structure, Quaternary; Protein Structure, Secondary; Protein Structure, Tertiary; Structure-Activity Relationship; Lipid-binding Protein; MxA Protein; G Proteins; GTP Hydrolysis; Innate Immunity; Antiviral Agents; Interferon; Dynamin-like
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.249037

The human MxA protein is an interferon-induced large GTPase with antiviral activity against a wide range of viruses, including influenza viruses. Recent structural data demonstrated that MxA oligomerizes into multimeric filamentous or ring-like structures by virtue of its stalk domain. Here, we show that negatively charged lipid membranes support MxA self-assembly. Like dynamin, MxA assembled around spherical liposomes inducing liposome tubulation. Cryo-transmission electron microscopy revealed that MxA oligomers around liposomes have a “T-bar” shape similar to dynamin. Moreover, biochemical assays indicated that the unstructured L4 loop of the MxA stalk serves as the lipid-binding moiety, and mutational analysis of L4 revealed that a stretch of four lysine residues is critical for binding. The orientation of the MxA molecule within the membrane-associated oligomer is in agreement with the proposed topology of MxA oligomers based on crystallographic data. Although oligomerization of wild-type MxA around liposomes led to the creation of helically decorated tubes similar to those formed by dynamin, this lipid interaction did not stimulate GTPase activity, in sharp contrast to the assembly-stimulated nucleotide hydrolysis observed with dynamin. Moreover, MxA readily self-assembles into rings at physiological conditions, as opposed to dynamin which self-assembles only at low salt conditions or onto lipids. Thus, the present results indicate that the oligomeric structures formed by MxA critically differ from those of dynamin.