分子灵活性在甲基转移酶MLL酶活调控中的作用机制探究

分子识别中的诱导契合和构象选择模型是目前流行的两种模型，指导着酶催化及调控领域的研究。MLL（Mixed Lineage Leukemia）家族蛋白是一类参与表观遗传调控、与癌症密切相关的组蛋白甲基转移酶，其活性受到若干结合蛋白的精确调控，但MLL和调控蛋白的相互作用究竟遵循哪种分子识别模型至今还存在争议，其催化活性调控的机制还未完全解析。本课题我们拟综合运用生物化学、生物物理、遗传筛选、结构生物学等手段，从提升MLL催化结构域的稳定性着手，分离鉴定具有单一构象的突变体，利用单分子技术考察其结构动态性与催化活性之间的联系，揭示这一类重要酶家族的活化模型，进一步加深对这类酶的性质及其调节规律的理解，希望所得的规律能够被用于指导以MLL为靶点的新型药物研发。同时，本研究将为较为新兴的构象选择模型提供新的实验证据，也为阐释蛋白质的稳定性、结构灵活性及生物活性的相互关系提供一定的帮助。

Molecular recognition is predominantly described by two alternative models: induced fit and conformational selection. Understanding and distinguishing the two processes is central to understand enzyme catalysis and regulation at the molecular lever. MLL (Mixed Lineage Leukemia) family of histone methyltransferases are the key players involved in epigenetic regulation. They participate in transcription activation and their malfunctions are closely associated with many human diseases including cancers. It is well known that the enzymatic activity of MLL is precisely regulated by several binding proteins, however, the mode of interaction between MLL and its regulatory proteins is still controversial and the precise mechanism for its activation is not fully resolved. In this proposal, we aim to understand the mode of action describing MLL’s activation using a combination of genetic selection, biochemical, biophysical, and structural biology techniques. We will obtain thermodynamically more stabilized mutants of the catalytic domain of MLL, and from these mutants screen for the ones that are locked in a single conformation using single molecular techniques. By comparing the methyltransferase activity of the mutants and their abilities to interact with MLL’s regulatory proteins, we hope to discover the relationship between stability, structural flexibility, and catalytic activity of the MLL proteins and the mode of action of the interaction between MLL and its regulatory proteins. Our research will not only provide some evidence for the newly established conformational selection model but also shed some light on novel drug design considering MLL as the target.