27 β-脱炭酸脱水素酵素の阻害剤設計(口頭発表の部)

抄録

Homoisocitrate dehydrogenase (HICDH) and 3-isopropylmalate dehydrogenase (IPMDH) belong to a unique family of bifunctional decarboxylating dehydrogenases. HICDH is involved in the α-aminoadipate pathway of L-lysine biosynthesis in higher fungi such as yeast and human pathogenic fungi. This enzyme catalyzes the oxidative decarboxylation of homoisocitrate into 2-ketoadipate using NAD^+ as a coenzyme. IPMDH is a key enzyme in L-leucine biosynthesis of microorganism and plants, and catalyzes the NAD^+ dependent oxidative decarboxylation of the substrate 3-isopropylmalate to 2-oxoisocaproate. Since L-lysine and L-leucine are essential amino acids for animal, these enzymes are considered to be a potential target for new antifungal and antimicrobial agents. Firstly, we designed and synthesized a series of aza-, oxa-, and thia-analogues of homoisocitrate as a potential inhibitor for HICDH as shown Fig. 3. Among them, thia-analogue showed a strong competitive inhibitory activity as K_i=97nM toward HICDH derived from Saccharomyces cerevisiae. Kinetic studies suggested that the formation of the keto-enolate intermediate played an important role in the inhibition. Based on this result, we also synthesized a series of aza-, oxa-, and thia-analogues as an inhibitor for IPMDH. As a result, thia-analogue was found to be a strong competitive inhibitor (K_i=64nM) toward IPMDH derived from Thermus thermophilus. In addition, T. thermophilus IPMDH-inhibitor-NAD^+ crystals were obtained and the structure showed that the product from thia-analogue inhibitor exited in the active site.