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<p>GM4951 is an immunity-related GTPase (IRG) that counteracts hepatic lipid accumulation in mice fed a high-fat diet. We determine full-length protein structures of GTPγS- and GDP-bound GM4951, and two missense mutants (N86K or D125G) associated with metabolic dysfunction-associated steatotic liver disease (MASLD) in mice. All four structures reveal a conserved GTPase domain fold and a helix bundle composed of the N- and C-terminal regions. Each mutation alters the dynamics of the switch-I and switch-II loops important for catalytic function and lipid droplet (LD) localization. GM4951 predominantly forms dimers in vitro. Cryo-electron microscopy reveals a dimer interface formed by the helical domains of two protomers (tail to tail), distinct from other IRGs. The N-terminal helices are necessary for LD localization, while a disulfide bond between helices in the GTPase domain and C-terminus&#xa0;is necessary for interaction with MASLD-associated HSD17B13. Distinct N- and C-terminal conformations set GM4951 apart from other IRGs structurally and functionally.</p>

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Structural insights into GM4951 as a lipid droplet GTPase regulating hepatic lipid metabolism

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月12日

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  • Rishi Raj,
  • Yiao Jiang,
  • Rahul Kumar Jha,
  • Eva Marie Y. Moresco,
  • Himanshu Joshi,
  • Zhao Zhang,
  • Bruce Beutler

摘要

GM4951 is an immunity-related GTPase (IRG) that counteracts hepatic lipid accumulation in mice fed a high-fat diet. We determine full-length protein structures of GTPγS- and GDP-bound GM4951, and two missense mutants (N86K or D125G) associated with metabolic dysfunction-associated steatotic liver disease (MASLD) in mice. All four structures reveal a conserved GTPase domain fold and a helix bundle composed of the N- and C-terminal regions. Each mutation alters the dynamics of the switch-I and switch-II loops important for catalytic function and lipid droplet (LD) localization. GM4951 predominantly forms dimers in vitro. Cryo-electron microscopy reveals a dimer interface formed by the helical domains of two protomers (tail to tail), distinct from other IRGs. The N-terminal helices are necessary for LD localization, while a disulfide bond between helices in the GTPase domain and C-terminus is necessary for interaction with MASLD-associated HSD17B13. Distinct N- and C-terminal conformations set GM4951 apart from other IRGs structurally and functionally.