Structural insights into the activation mechanism of antimicrobial GBP1

The dynamin-related human guanylate-binding protein 1 (GBP1) mediates host defenses against microbial pathogens. Upon GTP binding and hydrolysis, auto-inhibited GBP1 monomers dimerize and assemble into soluble and membrane-bound oligomers, which are crucial for innate immune responses. How higher-order GBP1 oligomers are built from dimers, and how assembly is coordinated with nucleotide-dependent conformational changes, has remained elusive. Here, we present cryo-electron microscopy-based structural data of soluble and membrane-bound GBP1 oligomers, which show that GBP1 assembles in an outstretched dimeric conformation. We identify a surface-exposed helix in the large GTPase domain that contributes to the oligomerization interface, and we probe its nucleotide- and dimerization-dependent movements that facilitate the formation of an antimicrobial protein coat on a gram-negative bacterial pathogen. Our results reveal a sophisticated activation mechanism for GBP1, in which nucleotide-dependent structural changes coordinate dimerization, oligomerization, and membrane binding to allow encapsulation of pathogens within an antimicrobial protein coat. Synopsis Oligomerization of the human guanylate-binding protein 1 (GBP1) mediates innate immune responses against bacterial pathogens. Here, structural analyses combined with biochemical experiments explain how nucleotide-dependent structural changes coordinate GBP1 oligomerization toward the formation of an antimicrobial protein coat. Cryo-EM shows that GBP1 assembles in an outstretched dimeric conformation to form soluble polymers and membrane-bound oligomers. The peripheral helix α4’ in the large GTPase domain is critical for establishing the oligomeric interface. Nucleotide-dependent structural changes coordinate GBP1 oligomerization and membrane binding to allow encapsulation of pathogens. GBP1 oligomerization and membrane binding are coordinated by nucleotide-dependent structural changes, facilitating the formation of a protein coat around bacteria.