Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
Commun Biol. 2024 Sep 28;7(1):1207. doi: 10.1038/s42003-024-06906-y.
Cyclopamine, a natural alkaloid, can act as an agonist when it binds to the Cysteine-Rich Domain (CRD) of Smoothened receptor and as an antagonist when it binds to the Transmembrane Domain (TMD). To study the effect of cyclopamine binding to each site experimentally, mutations in the other site are required. Hence, simulations are critical for understanding the WT activity due to binding at different sites. Using multi-milliseconds long aggregate MD simulations combined with Markov state models and machine learning, we explore the dynamic behavior of cyclopamine's interactions with different domains of WT SMO. A higher population of the active state at equilibrium, a lower free energy barrier of 2 kcal/mol, and expansion of hydrophobic tunnel to facilitate cholesterol transport agrees with cyclopamine's agonistic behavior when bound to CRD. A higher population of the inactive state at equilibrium, a higher free energy barrier of ~4 kcal/mol and restricted hydrophobic tunnel shows cyclopamine's antagonistic behavior when bound to TMD. With cyclopamine bound to both sites, there is a slightly larger inactive population at equilibrium and an increased free energy barrier (3.5 kcal/mol) exhibiting an overall weak antagonistic effect. These findings show cyclopamine's domain-specific modulation of SMO regulates Hedgehog signaling and cholesterol transport.
环巴胺是一种天然生物碱,当它与 Smoothened 受体的富含半胱氨酸结构域 (CRD) 结合时,可以作为激动剂,而当它与跨膜结构域 (TMD) 结合时,则作为拮抗剂。为了研究环巴胺与每个位点结合的实验效果,需要在另一个位点进行突变。因此,由于结合在不同的位点,模拟对于理解 WT 活性至关重要。我们使用长达数毫秒的聚合 MD 模拟,结合 Markov 状态模型和机器学习,来探索环巴胺与 WT SMO 不同结构域相互作用的动态行为。平衡时活性状态的更高种群、2 kcal/mol 的更低自由能势垒以及疏水隧道的扩张,有助于胆固醇的运输,这与环巴胺与 CRD 结合时的激动剂行为一致。平衡时,失活状态的种群更高,自由能势垒更高(4 kcal/mol),疏水隧道受到限制,表明环巴胺与 TMD 结合时具有拮抗作用。当环巴胺与两个位点结合时,平衡时失活种群稍大,自由能势垒增加(~3.5 kcal/mol),表现出总体较弱的拮抗作用。这些发现表明,环巴胺对 SMO 的特定结构域调节,控制 Hedgehog 信号和胆固醇运输。