1il0
From Proteopedia
X-RAY CRYSTAL STRUCTURE OF THE E170Q MUTANT OF HUMAN L-3-HYDROXYACYL-COA DEHYDROGENASE
Structural highlights
DiseaseHCDH_HUMAN Defects in HADH are the cause of 3-alpha-hydroxyacyl-CoA dehydrogenase deficiency (HADH deficiency) [MIM:231530. HADH deficiency is a metabolic disorder with various clinical presentations including hypoglycemia, hepatoencephalopathy, myopathy or cardiomyopathy, and in some cases sudden death. Defects in HADH are the cause of familial hyperinsulinemic hypoglycemia type 4 (HHF4) [MIM:609975; also known as persistent hyperinsulinemic hypoglycemia of infancy (PHHI) or congenital hyperinsulinism. HHF is the most common cause of persistent hypoglycemia in infancy and is due to defective negative feedback regulation of insulin secretion by low glucose levels. It causes nesidioblastosis, a diffuse abnormality of the pancreas in which there is extensive, often disorganized formation of new islets. Unless early and aggressive intervention is undertaken, brain damage from recurrent episodes of hypoglycemia may occur. HHF4 should be easily recognizable by analysis of acylcarnitine species and that this disorder responds well to treatment with diazoxide. It provides the first 'experiment of nature' that links impaired fatty acid oxidation to hyperinsulinism and that provides support for the concept that a lipid signaling pathway is implicated in the control of insulin secretion.[1] FunctionHCDH_HUMAN Plays an essential role in the mitochondrial beta-oxidation of short chain fatty acids. Exerts it highest activity toward 3-hydroxybutyryl-CoA. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedl-3-Hydroxyacyl-CoA dehydrogenase (HAD), the penultimate enzyme in the beta-oxidation spiral, reversibly catalyzes the conversion of l-3-hydroxyacyl-CoA to the corresponding 3-ketoacyl-CoA. Similar to other dehydrogenases, HAD contains a general acid/base, His(158), which is within hydrogen bond distance of a carboxylate, Glu(170). To investigate its function in this catalytic dyad, Glu(170) was replaced with glutamine (E170Q), and the mutant enzyme was characterized. Whereas substrate and cofactor binding were unaffected by the mutation, E170Q exhibited diminished catalytic activity. Protonation of the catalytic histidine did not restore wild-type activity, indicating that modulation of the pK(a) of His(158) is not the sole function of Glu(170). The pH profile of charge transfer complex formation, an independent indicator of active site integrity, was unaltered by the amino acid substitution, but the intensity of the charge transfer band was diminished. This observation, coupled with significantly reduced enzymatic stability of the E170Q mutant, implicates Glu(170) in maintenance of active site architecture. Examination of the crystal structure of E170Q in complex with NAD(+) and acetoacetyl-CoA (R = 21.9%, R(free) = 27.6%, 2.2 A) reveals that Gln(170) no longer hydrogen bonds to the side chain of His(158). Instead, the imidazole ring is nearly perpendicular to its placement in the comparable native complex and no longer positioned for efficient catalysis. Glutamate 170 of human l-3-hydroxyacyl-CoA dehydrogenase is required for proper orientation of the catalytic histidine and structural integrity of the enzyme.,Barycki JJ, O'Brien LK, Strauss AW, Banaszak LJ J Biol Chem. 2001 Sep 28;276(39):36718-26. Epub 2001 Jul 12. PMID:11451959[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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