Decarboxylase Structure-Function Relationships

所有吡哆醛脱辅基蛋白共有的结构特征 5 '-磷酸（PLP）依赖性羧化酶是一个活性位点 赖氨酸，其在β-氨基之间形成席夫碱， 基团和辅因子的醛部分。 二烷基 来自洋葱假单胞菌的甘氨酸脱羧酶（DGD）， 可能是这种酶。 它可以催化 脱羧和转氨反应。 以前的工作 表明质子转移是 不寻常. DGD催化质子转移到4'碳， 辅因子取代了氨基的α碳 酸 一个合理的假设是，决定指导方针在结构上是 与其他脱羧酶相似，但不同之处在于 反转组氨酸和赖氨酸的碱性。 这 改变会使溶剂质子优先 离辅因子4'碳更近的赖氨酸。 为了 为了测试这个模型的有效性， 用丙氨酸取代赖氨酸， 活性部位 如果实验结果证实了这一点 假设，它会告诉我们很多关于电 在活动现场的场强和如何这样的局部场 影响酶-底物自由能含量 配合物和过渡态。 凯勒医生很熟悉 而且受过良好训练 该项目将 对本科生质量有着重要影响 在东道机构接受教育。

A structural feature common to apoproteins of all pyridoxal 5'-phosphate (PLP) dependent carboxylases is an active site lysine which forms a Schiff base between the epsilon amino group and the aldehyde moiety of the cofactor. Dialkyl glycine decarboxylase (DGD) from Pseudomonas cepacia is probably such an enzyme. It can catalyze both decarboxylation and transamination reactions. Previous work with this enzyme suggests that the proton transfer is unusual. DGD catalyzes proton transfer to the 4' carbon of the cofactor instead of the alpha carbon of the amino acid. A reasonable hypothesis is that DGD is structurally similar to other decarboxylases but differs from them by inverting the basicities of histidine and lysine. This change would place the solvent proton preferentially on lysine which is closer to the cofactor 4' carbon. In order to test the validity of this model, mutants will be constucted with alanine substituting for the lysine at the active site. If the experimental outcome confirms this hypothesis, it will tell us a good deal about the electric field strengths at the active site and how such local fields affect the free energy contents of enzyme-substrates complexes and transition states. Dr. Keller is conversant with the enzyme and has been well trained. The project would have a fovarable impact on the quality of undergraduate education at the host institution.