title: Structural basis for L-lysine feedback inhibition of homocitrate synthase.
abstract: The alpha-aminoadipate pathway of lysine biosynthesis is modulated at the transcriptional and biochemical levels by feedback inhibition. The first enzyme in the alpha-aminoadipate pathway, homocitrate synthase (HCS), is the target of the feedback regulation and is strongly inhibited by l-lysine. Here we report the structure of Schizosaccharomyces pombe HCS (SpHCS) in complex with l-lysine. The structure illustrates that the amino acid directly competes with the substrate 2-oxoglutarate for binding within the active site of HCS. Differential recognition of the substrate and inhibitor is achieved via a switch position within the (alpha/beta)(8) TIM barrel of the enzyme that can distinguish between the C5-carboxylate group of 2-oxoglutarate and the epsilon-ammonium group of l-lysine. In vitro and in vivo assays demonstrate that mutations of the switch residues, which interact with the l-lysine epsilon-ammonium group, abrogate feedback inhibition, as do substitutions of residues within the C-terminal domain that were identified in a previous study of l-lysine-insensitive HCS mutants in Saccharomyces cerevisiae. Together, these results yield new insights into the mechanism of feedback regulation of an enzyme central to lysine biosynthesis.
authors.affiliation: Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Stacie L
authors.initials: SL
authors.lastname: Bulfer
authors.forename: Erin M
authors.initials: EM
authors.lastname: Scott
authors.forename: Lorraine
authors.initials: L
authors.lastname: Pillus
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Trievel
mesh_terms: D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D025461:Feedback, Physiological; D007656:Ketoglutaric Acids / Q000378:metabolism; D008239:Lysine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D007652:Oxo-Acid-Lyases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D012568:Schizosaccharomyces / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*
chemical_list: D007656:Ketoglutaric Acids; C021365:homocitrate synthase; D007652:Oxo-Acid-Lyases; D008239:Lysine