Chang Shenghai, Wang Weiwei, Madigan Michael T, Yu Long-Jiang, Gao Haichun, Wang-Otomo Zheng-Yu, Zhang Xing, Chen Jing-Hua
Department of Biophysics, Department of Pathology of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, Zhejiang, China.
Center of Cryo-Electron Microscopy, Zhejiang University School of Medicine, Hangzhou, 310058, Zhejiang, China.
Sci Rep. 2025 Jul 2;15(1):22941. doi: 10.1038/s41598-025-07081-8.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) catalyzes the initial carbon fixation reaction in the Calvin-Benson-Bassham cycle. Among the many forms of RuBisCOs, form-I-a protein complex containing 8 large and 8 small subunits-is the most common, representing over 90% of all known RuBisCOs. Although many form-I RuBisCO structures have been determined, no structure has been reported for a form-IAq RuBisCO. Here, we detail the structure of the heat-stable form-IAq RuBisCO from the thermophilic and anaerobic purple bacterium Thermochromatium (Tch.) tepidum at 1.55 Å resolution. The overall structure of the Tch. tepidum form-IAq RuBisCO resembles both a form-IAc RuBisCO from a chemolithotrophic sulfur bacterium and a synthetic form-I RuBisCO reconstructed from ancestral sequences. However, the Tch. tepidum enzyme shows significantly greater interactions between adjacent small subunits through their extended N-terminal domains that contain a characteristic six-residue insertion unique to form-IAq RuBisCOs. Structural differences of Tch. tepidum RuBisCO from its mesophilic relative Allochromatium vinosum, and key substitutions on the hydrophilic surface of the small subunits suggests the mechanisms of its enhanced thermostability. Our structure represents the first structure of a form-IAq RuBisCO, providing fresh clues for unraveling the evolutionary history of RuBisCO and new details for how this key enzyme remains active at elevated temperatures.
核酮糖-1,5-二磷酸羧化酶/加氧酶（RuBisCO）催化卡尔文-本森-巴斯姆循环中的初始碳固定反应。在众多形式的RuBisCO中，由8个大亚基和8个小亚基组成的I-a型蛋白质复合物最为常见，占所有已知RuBisCO的90%以上。尽管已经确定了许多I型RuBisCO的结构，但尚未有IAq型RuBisCO的结构报道。在此，我们详细阐述了嗜热厌氧紫色细菌嗜温嗜热色菌（Tch.）tepidum中热稳定的IAq型RuBisCO的结构，分辨率为1.55 Å。嗜温嗜热色菌IAq型RuBisCO的整体结构既类似于化能自养硫细菌的IAc型RuBisCO，也类似于由祖先序列重建的合成I型RuBisCO。然而，嗜温嗜热色菌的这种酶通过其延伸的N端结构域在相邻小亚基之间显示出明显更强的相互作用，该结构域包含IAq型RuBisCO特有的一个特征性六残基插入序列。嗜温嗜热色菌RuBisCO与其嗜温近亲嗜酒色菌的结构差异，以及小亚基亲水表面上的关键取代，揭示了其增强热稳定性的机制。我们的结构代表了IAq型RuBisCO的首个结构，为揭示RuBisCO的进化历史提供了新线索，并为这种关键酶在高温下如何保持活性提供了新细节。
