1ZMD: Crystal Structure Of Human Dihydrolipoamide Dehydrogenase Complexed To Nadh

Citation:
Abstract
Human dihydrolipoamide dehydrogenase (hE3) is an enzymatic component common to the mitochondrial alpha-ketoacid dehydrogenase and glycine decarboxylase complexes. Mutations to this homodimeric flavoprotein cause the often-fatal human disease known as E3 deficiency. To catalyze the oxidation of dihydrolipoamide, hE3 uses two molecules: non-covalently bound FAD and a transiently bound substrate, NAD+. To address the catalytic mechanism of hE3 and the structural basis for E3 deficiency, the crystal structures of hE3 in the presence of NAD+ or NADH have been determined at resolutions of 2.5A and 2.1A, respectively. Although the overall fold of the enzyme is similar to that of yeast E3, these two structures differ at two loops that protrude from the proteins and at their FAD-binding sites. The structure of oxidized hE3 with NAD+ bound demonstrates that the nicotinamide moiety is not proximal to the FAD. When NADH is present, however, the nicotinamide base stacks directly on the isoalloxazine ring system of the FAD. This is the first time that this mechanistically requisite conformation of NAD+ or NADH has been observed in E3 from any species. Because E3 structures were previously available only from unicellular organisms, speculations regarding the molecular mechanisms of E3 deficiency were based on homology models. The current hE3 structures show directly that the disease-causing mutations occur at three locations in the human enzyme: the dimer interface, the active site, and the FAD and NAD(+)-binding sites. The mechanisms by which these mutations impede the function of hE3 are discussed.
PDB ID: 1ZMDDownload
MMDB ID: 33898
PDB Deposition Date: 2005/5/10
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 2.08  Å
Source Organism:
Similar Structures:
Biological Unit for 1ZMD: dimeric; determined by author and by software (PISA)
Molecular Components in 1ZMD
Label Count Molecule
Proteins (2 molecules)
2
Dihydrolipoyl Dehydrogenase(Gene symbol: DLD)
Molecule annotation
Chemicals (11 molecules)
1
7
2
2
3
2
* Click molecule labels to explore molecular sequence information.

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