Structural highlights
Publication Abstract from PubMedCitrate synthase (CS) catalyzes the formation of citrate and coenzyme A from acetyl-CoA and oxaloacetate. CS exists in two forms: type I and type II. We determined the citrate-bound crystal structure of type II CS from the Hymenobacter sp. PAMC 26554 bacterium (HyCS; isolated from Antarctic lichen). Citrate molecules bound to a cleft between the large and small domains of HyCS. Structural comparison of HyCS with other type II CSs revealed that type II CSs have a highly conserved flexible hinge region (residues G264-P265 in HyCS), enabling correct positioning of active site residues. Notably, the catalytic His266 residue of HyCS interacted with Trp262 in the inactive (unliganded open) state of other type II CSs, whereas the His266 residue moved to the active site via a small-domain swing motion, interacting with the bound citrate in the closed conformation of HyCS. However, type I CSs lack this tryptophan residue and face-to-edge interactions. Thus, type II CSs might have a unique domain-motion control mechanism enabling a tight allosteric regulation. An activity assay using a W262A mutant showed a Hill coefficient of 2.4; thus, the interaction between Trp262 and His266 was closely related to the positive cooperative ligand binding of type II CS. Structural basis of the cooperative activation of type II citrate synthase (HyCS) from Hymenobacter sp. PAMC 26554.,Park SH, Lee CW, Bae DW, Do H, Jeong CS, Hwang J, Cha SS, Lee JH Int J Biol Macromol. 2021 Jul 31;183:213-221. doi:, 10.1016/j.ijbiomac.2021.04.141. Epub 2021 Apr 25. PMID:33910038[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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