human polycomb 2 protein is a sumo e3 ligase and alleviates substrate-induced inhibition of cystathionine β-synthase sumoylation人类polycomb 2蛋白质是一个相扑e3连接酶和减轻substrate-induced抑制胱硫醚β-synthase sumoylation.pdfVIP

Human Polycomb 2 Protein Is a SUMO E3 Ligase and Alleviates Substrate-Induced Inhibition of Cystathionine b-Synthase Sumoylation Nitish Agrawal, Ruma Banerjee* Department of Biological Chemistry, School of Medicine, University of Michigan, Ann Arbor, Michigan, United States of America Abstract Human cystathionine b-synthase (CBS) catalyzes the first irreversible step in the transsulfuration pathway and commits homocysteine to the synthesis of cysteine. Mutations in CBS are the most common cause of severe hereditary hyperhomocysteinemia. A yeast two-hybrid approach to screen for proteins that interact with CBS had previously identified several components of the sumoylation pathway and resulted in the demonstration that CBS is a substrate for sumoylation. In this study, we demonstrate that sumoylation of CBS is enhanced in the presence of human polycomb group protein 2 (hPc2), an interacting partner that was identified in the initial yeast two-hybrid screen. When the substrates for CBS, homocysteine and serine for cystathionine generation and homocysteine and cysteine for H2S generation, are added to the sumoylation mixture, they inhibit the sumoylation reaction, but only in the absence of hPc2. Similarly, the product of the CBS reaction, cystathionine, inhibits sumoylation in the absence of hPc2. Sumoylation in turn decreases CBS activity by ,28% in the absence of hPc2 and by 70% in its presence. Based on these results, we conclude that hPc2 serves as a SUMO E3 ligase for CBS, increasing the efficiency of sumoylation. We also demonstrate that c-cystathionase, the second enzyme in the transsulfuration pathway is a substrate for sumoylation under in vitro conditions. We speculate that the role of this modification may be for nuclear localization of the cysteine-generat