Wang Rong, Chen Baozhi, Elghobashi-Meinhardt Nadia, Tie Jian-Ke, Ayala Alyssa, Zhou Ning, Qi Xiaofeng
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Nature. 2025 Mar;639(8055):808-815. doi: 10.1038/s41586-024-08484-9. Epub 2025 Jan 29.
γ-Glutamyl carboxylase (GGCX) is the sole identified enzyme that uses vitamin K (VK) as a cofactor in humans. This protein catalyses the oxidation of VK hydroquinone to convert specific glutamate residues to γ-carboxyglutamate residues in VK-dependent proteins (VDPs), which are involved in various essential biological processes and diseases. However, the working mechanism of GGCX remains unclear. Here we report three cryogenic electron microscopy structures of human GGCX: in the apo state, bound to osteocalcin (a VDP) and bound to VK. The propeptide of the VDP binds to the lumenal domain of GGCX, which stabilizes transmembrane helices 6 and 7 of GGCX to create the VK-binding pocket. After binding of VK, residue Lys218 in GGCX mediates the oxidation of VK hydroxyquinone, which leads to the deprotonation of glutamate residues and the construction of γ-carboxyglutamate residues. Our structural observations and results from binding and cell biological assays and molecular dynamics simulations show that a cholesterol molecule interacts with the transmembrane helices of GGCX to regulate its protein levels in cells. Together, these results establish a link between cholesterol metabolism and VK-dependent pathways.
γ-谷氨酰羧化酶（GGCX）是人类唯一已确定的以维生素K（VK）作为辅因子的酶。该蛋白质催化VK对苯二酚的氧化，将特定的谷氨酸残基转化为VK依赖性蛋白质（VDPs）中的γ-羧基谷氨酸残基，这些蛋白质参与各种重要的生物过程和疾病。然而，GGCX的工作机制仍不清楚。在此，我们报告了人类GGCX的三种低温电子显微镜结构：无辅因子状态、与骨钙素（一种VDP）结合状态以及与VK结合状态。VDP的前肽与GGCX的腔结构域结合，稳定GGCX的跨膜螺旋6和7，从而形成VK结合口袋。VK结合后，GGCX中的赖氨酸218残基介导VK对苯二酚的氧化，导致谷氨酸残基去质子化并形成γ-羧基谷氨酸残基。我们的结构观察结果以及结合和细胞生物学实验结果与分子动力学模拟表明，一个胆固醇分子与GGCX的跨膜螺旋相互作用，以调节其在细胞中的蛋白质水平。总之，这些结果建立了胆固醇代谢与VK依赖性途径之间的联系。
