COMPUTER SIMULATIONS OF ENZYMES AND DNA

来自实验的信息是必要的，但通常不足以描述酶和DNA中化学反应的机制和能量学。最近开发的pseudobond量子力学/分子力学方法将被应用于模拟酶和DNA的反应;选择这些系统是因为它们内在的生物医学利益，实验结构数据的可用性作为出发点，以及与实验室研究系统并继续这样做的研究人员建立的合作。该项目的长期目标是开发和建立基于DFT的QM/MM模拟，作为研究酶和DNA中结构和化学反应的实验的合作伙伴，并提供对生物系统中化学反应机制的洞察。（1）4-草醛酸互变异构酶（4-Oxalocrontonate tautomerase，4 OT）是一类以氨基末端脯氨酸为总碱基的酶。实验研究仅提供了4 OT的反应机理的原始图像。伪键QM/MM自由能方法将被用来探索4 OT的机制细节，并提供实验观察的理解。(2)环核苷酸磷酸二酯酶（cyclicnucleotidephosphodiesterases，PDE）是一类组成多样性超家族的酶，通过水解最常见的第二信使环腺苷酸（cyclicadenosine monophosphate，cAMP）和环鸟苷酸（cyclicguanosine monophosphate，cGMP），在细胞信号传递中发挥重要作用。PDE的选择性抑制剂具有潜在的治疗价值。我们建议研究PDE 4水解cAMP的机制，以解决该机制是缔合的还是解离的，并为抑制剂设计提供见解和指导。(3)腈水合酶（Nitrile hydratase，简称NHase）是一种催化腈水合的细菌金属酶，是工业上最成功的酶之一。关于这个活性中心的重要结构和机制细节仍然不清楚。拟键QM/MM方法将用于确定其活性中心的结构，研究Fe（III）中心这种独特的自旋偏好的结构基础，并探索催化反应机理。(4)核酸的化学反应性，特别是核碱基氧化反应，对于理解DNA和RNA自然受损，导致衰老和癌症的机制具有内在的意义。伪键QM/MM方法将被应用于研究DNA中鸟嘌呤的氧化反应，导致的机制和电子结构的定量描述。(5)进一步的方法发展将集中在设计的有效核心潜力的碳边界原子在C-N单键的DNA计算。

Information from experiments is necessary, but often insufficient to characterize the mechanisms and energetics of chemical reactions in enzymes and DNA. The recently developed pseudobond quantum mechanical/molecular mechanical approach will be applied to simulate the reactions in enzymes and DNA; the systems are chosen because of their intrinsic biomedical interests, the availability of experimental structural data as starting point, and the collaborations established with investigators whose laboratories have investigated the systems and continue to do so. The long- term goal of this project is to develop and establish the DFT-based QM/MM simulation as a partner equal to experiments for the study of structure and chemical reactions in enzymes and DNA and to provide insight into the chemical reaction mechanisms in biological systems. The following are the specific tasks of this project: (1) 4-Oxalocrontonate tautomerase (4OT) belongs to a family of enzymes which use their amino-terminal proline as a general base in catalysis. Experimental studies have only provided a primitive picture of the reaction mechanism of 4OT. The pseudobond QM/MM free energy approach will be employed to explore the mechanistic details of 4OT and provide understanding of the experimental observations. (2) Cyclic nucleotide phosphodiesterases(PDE) are enzymes forming a diverse super family and play fundamental roles in cell signal transfer by their common activity of hydrolyzing the most common second messengers 3',5'-cyclic adenosine monophosphate(cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP). Selective inhibitors of PDEs are of potential therapeutic values. We propose to study the mechanism by which PDE4 hydrolyze cAMP, to address whether the mechanism is associative or dissociative, and to provide insight and guide to inhibitor design. (3) Nitrile hydratase (NHase), a bacterial metalloenzyme catalyzing the hydration of nitriles, is well-known as one of the most industrially successful enzymes. Important structural and mechanistic details concerning this active center is still not clear. The pseudobond QM/MM method will be employed to determine the structure of its active site, study the structure basis for this unique spin-preference of Fe (III) center and explore the catalytic reaction mechanisms. (4) The chemical reactivity of nucleic acids, in particular, nucleobase oxidation reactions, is of intrinsic interest in understanding the mechanisms by which DNA and RNA is naturally damaged, leading to aging and cancer. The pesudobond QM/MM methods will be applied to investigate the guanine oxidation reactions in DNA, leading to a quantitative description of the mechanism and electronic structure. (5) Further methodology development will focus on the design of the effective core potential for the carbon boundary atom in the C-N single bond for DNA calculations.