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Isopropylmalate synthase binding with ketoisovalerateIsopropylmalate synthase binding with ketoisovalerate
Structural highlights
Publication Abstract from PubMedThe committed step of leucine biosynthesis, converting acetyl-CoA and alpha-ketoisovalerate into alpha-isopropylmalate, is catalyzed by alpha-isopropylmalate synthase (IPMS), an allosteric enzyme subjected to feedback inhibition by the end product L-leucine. We characterized the short form IPMS from Leptospira biflexa (LbIPMS2), which exhibits a catalytic activity comparable with that of the long form IPMS (LbIPMS1) and has a similar N-terminal domain followed by subdomain I and subdomain II but lacks the whole C-terminal regulatory domain. We found that partial deletion of the regulatory domain of LbIPMS1 resulted in a loss of about 50% of the catalytic activity; however, when the regulatory domain was deleted up to Arg-385, producing a protein that is almost equivalent to the intact LbIPMS2, about 90% of the activity was maintained. Moreover, in LbIPMS2 or LbIPMS1, further deletion of several residues from the C terminus of subdomain II significantly impaired or completely abolished the catalytic activity, respectively. These results define a complete and independently functional catalytic module of IPMS consisting of both the N-terminal domain and the two subdomains. Structural comparison of LbIPMS2 and the Mycobacterium tuberculosis IPMS revealed two different conformations of subdomain II that likely represent two substrate-binding states related to cooperative catalysis. The biochemical and structural analyses together with the previously published hydrogen-deuterium exchange data led us to propose a conformation transition mechanism for feedback inhibition mediated by subdomains I and II that might associated with alteration of the binding affinity toward acetyl-CoA. Subdomain II of alpha-isopropylmalate synthase is essential for activity: inferring a mechanism of feedback inhibition.,Zhang Z, Wu J, Lin W, Wang J, Yan H, Zhao W, Ma J, Ding J, Zhang P, Zhao GP J Biol Chem. 2014 Oct 3;289(40):27966-78. doi: 10.1074/jbc.M114.559716. Epub 2014, Aug 15. PMID:25128527[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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