Guanylate-binding proteins (GBPs) are interferon-inducible guanosine triphosphate hydrolases (GTPases) mediating host defense against intracellular pathogens. Their antimicrobial activity hinges on their ability to self-associate and coat pathogen-associated compartments or cytosolic bacteria. Coat formation depends on GTPase activity but how nucleotide binding and hydrolysis prime coat formation remains unclear. Here, we report the cryo-electron microscopy structure of the full-length human GBP1 dimer in its guanine nucleotide-bound state and describe the molecular ultrastructure of the GBP1 coat on liposomes and bacterial lipopolysaccharide membranes. Conformational changes of the middle and GTPase effector domains expose the isoprenylated C terminus for membrane association. The α-helical middle domains form a parallel, crossover arrangement essential for coat formation and position the extended effector domain for intercalation into the lipopolysaccharide layer of gram-negative membranes. Nucleotide binding and hydrolysis create oligomeric scaffolds with contractile abilities that promote membrane extrusion and fragmentation. Our data offer a structural and mechanistic framework for understanding GBP1 effector functions in intracellular immunity.

Mammalian cells have acquired a repertoire of defense strategies to deal with intracellular pathogens summarized as cell-autonomous immunity. In this thesis we studied one family of interferon inducible effector proteins involved in this process called guanylate binding proteins (GBPs). GBPs have been shown to combat a broad variety of pathogens including bacteria, viruses and protozoa. Due to their important antimicrobial role we used a structural approach to better understand the underlying oligomerization properties of GBPs, their organization on membranes as well as the functional implication originating from membrane binding...