Integrative dynamic structural biology unveils conformers essential for the oligomerization of a large GTPase

TL;DR

This study uses integrative dynamic structural biology techniques to reveal the conformational flexibility and mechanisms underlying GTP-controlled oligomerization of human GBP1, a protein involved in immune defense.

Contribution

It provides the first detailed dynamic structural characterization of GBP1 conformers essential for its oligomerization process.

Findings

Identified GTP-independent flexibility in the C-terminal effector domain.

Characterized conformers that enable GBP1 to open like a pocketknife.

Unveiled GTP-triggered domain association and assembly-dependent GTP hydrolysis.

Abstract

Guanylate binding proteins (GBPs) are soluble dynamin-like proteins with structured domains that undergo a conformational transition for GTP-controlled oligomerization to exert their function as part of the innate immune system of mammalian cells - attacking intra-cellular parasites by disrupting their membranes. The structural basis and mechanism of this process is unknown. Therefore, we apply neutron spin echo, X-ray scattering, fluorescence, and EPR spectroscopy as techniques for integrative dynamic structural biology to human GBP1 (hGBP1). We mapped hGBP1's essential dynamics from nanoseconds to milliseconds by motional spectra of sub-domains. We find a GTP-independent flexibility of the C-terminal effector domain in the $\mu$s-regime and structurally characterize conformers being essential that hGBP1 can open like a pocketknife for oligomerization. This unveils the intrinsic flexibility, a GTP-triggered association of the GTPase-domains and assembly-dependent GTP-hydrolysis as functional design principles of hGBP1 that control its reversible oligomerization in polar assemblies and the subsequent formation of condensates.