Crystal structures reveal nucleotide-induced conformational changes in G motifs and distal regions in human guanylate-binding protein 2

Guanylate-binding proteins (GBPs) are interferon-inducible GTPases that confer protective immunity against a variety of intracellular pathogens. GBP2 is one of the two highly inducible GBPs, yet the precise mechanisms underlying the activation and regulation of GBP2, in particular the nucleotide-induced conformational changes in GBP2, remain poorly understood. In this study, we elucidate the structural plasticity of GBP2 upon nucleotide binding through crystallographic analysis. By determining the crystal structures of GBP2 G domain (GBP2GD) in complex with GDP and nucleotide-free full-length GBP2 with K51A mutation (GBP2^K51A), we unveil distinct conformational states adopted by the nucleotide-binding pocket and distal regions of the protein. Comparison between the nucleotide-free full-length GBP2^K51A structure with homologous structures reveals notable movement in the C-terminal helical region, along with conformational changes in the G domain. Through comparative analysis, we identify subtle but critical differences in the nucleotide-bound states of GBP2, providing insights into the molecular basis of its dimer-monomer transition and enzymatic activity. These findings pave the way for future investigations aimed at elucidating the precise molecular mechanisms underlying GBP2's role in the immune response and open avenues for exploring how the unique functions of GBPs could be leveraged to combat pathogen invasion.