手性β-羟基-α-氨基酸是很多药物合成的关键中间体，实现其高效手性合成一直是研究的热点之一。L-苏氨酸醛缩酶在温和反应条件下，催化甘氨酸和醛底物缩合，生成具有两个手性碳的β-羟基-α-氨基酸产物。产物α-碳的立体选择性能够得到绝对控制，但β-碳的立体选择性则往往不高，导致合成的产物为混合物形式，限制了L-苏氨酸醛缩酶在合成方面的应用。本项目以实验室已获得的L-苏氨酸醛缩酶作为研究对象，测试不同的反应底物生成产物β-碳的立体构型，以酶的晶体结构作为基础，获得底物分子、辅因子与酶分子相互作用信息，发现β-碳立体选择性控制的影响因素，对酶分子进行半理性设计，验证推测的β-碳立体选择性影响因素的正确性，从而解析L-苏氨酸醛缩酶对β-碳的立体选择性控制的机理，提高催化过程中产物β-碳的立体选择性。利用获得的有益突变体作为催化剂，合成高光学纯的β-羟基-α-氨基酸，为该酶的进一步研究和应用打下基础。

Chiral β-hydroxy-α-amino acids are very important intermediates for the synthesis of pharmaceuticals. Effective methods have been continuously sought for the preparation of these highly valuable compounds. L-Threonine aldolase (L-TA) catalyzes the aldol reaction of aldehydes and glycine to produce β-hydroxy-α-amino acids in one-step, offering an attractive approach to access these compounds. While the enzyme has excellent stereocontrol at the α-carbon of the product β-hydroxy-α-amino acid, low or moderate stereoselectivity is often observed at the β-carbon. As such, the product is usually a mixture of two stereomers, limiting its synthetic application. We have obtained 10 L-threonine aldolases of different origins. The project will study the β-carbon stereoselectivity of these L-threonine aldolases toward different aldehyde substrates. Based on the structures of some L-TAs, mutagenesis and property studies in combination with molecular modeling and calculation will be employed to investigate the relationship between the structure of L-TA and β-carbon stereoselectivity, thus revealing the β-carbon stereocontrol mechanism of L-threonine aldolase. Based on these results, the L-TA will be rational designed and some mutant enzymes, which show high stereoselectivity at β-carbon, will be tested for the synthesis of some important β-hydroxy-α-amino acids.