Comparison of the molecular structures of cytoplasmic and mitochondrial malate dehydrogenase.
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Animals↗
Biomedical subjects
S L Roderick
Publications and source records attributed to S L Roderick.
Crystallization of methionine aminopeptidase from Escherichia coli.
Crystals of methionine aminopeptidase from Escherichia coli have been obtained. The crystals are of space group P2(1) with unit cell dimensions a = 39.3 A, b = 62.6 A, c = 54.3 A, beta = 107.8 degrees and diffract to 2.1-A resolution. They contain one polypeptide chain in the asymmetric unit and are suitable for a high resolution crystallographic study.
Aminopeptidases↗
Comparison of the precursor and mature forms of rat heart mitochondrial malate dehydrogenase.
The complete amino acid sequence of mitochondrial malate dehydrogenase from rat heart has been determined by chemical methods. Peptides used in this study were purified after digestions with cyanogen bromide, trypsin, endoproteinase Lys C, and staphylococcal protease V-8. The amino acid sequence of this mature enzyme is compared with that of the precursor form, which includes the primary structure of the transit peptide. The transit peptide is required for incorporation into mitochondria and appears to be homologous to the NH2-terminal arm of a related cytoplasmic enzyme, pig heart lactate dehydrogenase. The amino acid differences between the rat heart and pig heart mitochondrial malate dehydrogenases are analyzed in terms of the three-dimensional structure of the latter. Only 12/314 differences are found; most are conservative changes, and all are on or near the surface of the enzyme. We propose that the transit peptide is located on the surface of the mitochondrial malate dehydrogenase precursor.
Amino Acid Sequence↗
The three-dimensional structure of porcine heart mitochondrial malate dehydrogenase at 3.0-A resolution.
In a previous study, we reported the apparent similarity between a low resolution electron density map of mitochondrial malate dehydrogenase and a model of cytoplasmic malate dehydrogenase (Roderick, S. L., and Banaszak, L. J. (1983) J. Biol. Chem. 258, 11636-11642). We have since determined the polypeptide chain conformation and coenzyme binding site of crystalline porcine heart mitochondrial malate dehydrogenase by x-ray diffraction methods. The crystals from which the diffraction data was obtained contain four subunits of the enzyme arranged as a "dimer of dimers," resulting in a crystalline tetramer which possesses 222 molecular symmetry. The overall polypeptide chain conformation of the enzyme, the location of the coenzyme binding site, and the preliminary location of several catalytically important residues have confirmed the structural similarity of mitochondrial malate dehydrogenase to cytoplasmic malate dehydrogenase and lactate dehydrogenase.
Animals↗
The conformation of mitochondrial malate dehydrogenase derived from an electron density map at 5.3-A resolution.
A monoclinic form of crystalline porcine heart mitochondrial malate dehydrogenase has been prepared and contains two dimers in the asymmetric unit. The analysis of single crystal x-ray data shows that the two dimers are packed in the crystal lattice as a tetramer with approximate 222-point symmetry. Heavy atom derivatives using the compounds ethylmercurithiosalicylic acid and IrCl3 have been characterized and multiple isomorphous replacement methods have been used to obtain an electron density map at 5.3-A resolution. The phasing of the x-ray data was aided by including contributions from crystal forms with and without the coenzyme, NAD+. By using electron density averaging methods, the quality of the low resolution electron density map was improved to the point where it was possible to establish the overall conformation of mitochondrial malate dehydrogenase. The results confirm the proposed similarities between the mitochondrial and cytoplasmic forms of the malate dehydrogenases. Studies using x-ray data from the apo- and holo-forms of the enzyme describe the location of the active site as well as the arrangement of subunits in the tetrameric crystalline form of the enzyme.
Animals↗