Interferons play essential roles in innate immunity, stimulating synthesis of numerous proteins required for intracellular defence against pathogens. These include proteins such as nitric oxide synthase 2 (NOS2/iNOS) and dsRNA-dependent protein kinase (PKR), as well as several GTPases. Members of the 47 kDa GTPase family, for example, are essential for protection from certain intracellular pathogens; however, their precise roles are unclear. Jens Zerrahn and co-workers have therefore investigated the function of a γ-interferon-inducible member of this family, IIGP (see ). Intriguingly, they find that IIGP interacts in two-hybrid assays with hook 3 – a microtubule-binding linker protein implicated in membrane trafficking. The authors use coimmunoprecipitation and fluorescence microscopy to show that this interaction occurs in vivo on Golgi membranes. They also demonstrate that IIGP must be GTP bound to interact with hook 3 and use deletion mutants to examine the regions of the proteins that interact. Their findings suggest that IIGP somehow regulates intracellular membrane trafficking. It could, for instance, target endosomal/phagosomal compartments in which pathogens reside, promoting degradation of their contents, or interfere with nutrient provision.
