Subunit Of Pyruvate Dehydrogenase Complex Research Articles

Purification and acetylation of protein X subunit of pyruvate dehydrogenase complex (PDC) from bovine kidney

Protein X is one of the subunits of pyruvate dehydrogenase complex. The biological role of this protein has not been fully elucidated, mainly because of the difficulty in its dissociation from the tightly bound dihydrolipoamide acetyltransferase-protein X subcomplex. We have found that the detachment of protein X from acetyltransferase subunit can be easily accomplished by the cycles of freezing and thawing process. Several lines of evidence including sodium dodecyl sulfate-polyacrylamide gel electrophoresis, N-terminal amino acid sequence analysis and acetylation with [2-14C] pyruvate confirmed that the purified protein is protein X. The purified intact form of protein X was acetylated by [2-14C] pyruvate in the presence of pyruvate dehydrogenase subunit. The acetylation efficiency of this protein was lower than that of acetyltransferase and was not affected by the presence of acetyltransferase.

Epitope mapping and reactivity of autoantibodies to the E2 component of 2-oxoglutarate dehydrogenase complex in primary biliary cirrhosis using recombinant 2-oxoglutarate dehydrogenase complex

Five different target mitochondrial autoantigens recognized by sera from patients with primary biliary cirrhosis (PBC) have been identified as subunits of the following 2-oxo acid dehydrogenase complexes: the pyruvate dehydrogenase complex (PDC), the branched chain 2-oxo acid dehydrogenase complex (BCOADC), and the 2-oxoglutarate dehydrogenase complex (OGDC). Unlike the E2 subunits of PDC (PDC-E2) and BCOADC (BCOADC-E2), the E2 subunits of OGDC (OGDC-E2) reactivity of PBC sera and the reactive epitope of OGDC-D2 have not hitherto been studied in detail. In this report, we took advantage of a recombinant fusion protein for OGDC-E2 to address these issues. Eighty of 268 (29.9%) PBC patient sera but none of the 45 controls reacted with recombinant OGDC-E2. The recombinant OGDC-E2 was judged to express the immunodominant epitope, because when sera from patients with PBC were preabsorbed with the recombinant fusion protein, such sera were depleted of reactivity against 48 kD OGDC-E2 when probed on beef heart mitochondria (BHM) but retained reactivity toward PDC-E2 and/or BCOADC-E2. Furthermore, affinity-purified PBC sera against recombinant OGDC-E2 reacted only with native OGDC-E2 and not with any other enzyme components of the 2-oxo acid dehydrogenase complex. Antimitochondrial autoantibodies (AMA) against OGDC-E2 included immunoglobulin (Ig)G2, IgG3 and IgM and the relative titers were as follows: IgG2 > IgG3 > IgM. Finally, using overlapping recombinant polypeptides, it was determined that a minimum of 81 amino acids (residues 67-147) corresponding to the lipoyl domain of OGDC-E2 are necessary for reactivity, suggesting that a conformational autoepitope is recognized by AMA. These data suggest that each of the 2-oxo acid dehydrogenase enzymes has distinct antigenicity despite their similarities in structure and function. The availability of recombinant OGDC-E2 autoantigen will allow the design of additional studies to further our understanding of the role of mitochondrial autoantigens in the pathogenesis of PBC.

Epitope mapping and reactivity of autoantibodies to the E2 component of 2-oxoglutarate dehydrogenase complex in primary biliary cirrhosis using recombinant 2-oxoglutarate dehydrogenase complex

Five different target mitochondrial autoantigens recognized by sera from patients with primary biliary cirrhosis (PBC) have been identified as subunits of the following 2-oxo acid dehydrogenase complexes: the pyruvate dehydrogenase complex (PDC), the branched chain 2-oxo acid dehydrogenase complex (BCOADC), and the 2-oxoglutarate dehydrogenase complex (OGDC). Unlike the E2 subunits of PDC (PDC-E2) and BCOADC (BCOADC-E2), the E2 subunits of OGDC (OGDC-E2) reactivity of PBC sera and the reactive epitope of OGDC-D2 have not hitherto been studied in detail. In this report, we took advantage of a recombinant fusion protein for OGDC-E2 to address these issues. Eighty of 268 (29.9%) PBC patient sera but none of the 45 controls reacted with recombinant OGDC-E2. The recombinant OGDC-E2 was judged to express the immunodominant epitope, because when sera from patients with PBC were preabsorbed with the recombinant fusion protein, such sera were depleted of reactivity against 48 kD OGDC-E2 when probed on beef heart mitochondria (BHM) but retained reactivity toward PDC-E2 and/or BCOADC-E2. Furthermore, affinity-purified PBC sera against recombinant OGDC-E2 reacted only with native OGDC-E2 and not with any other enzyme components of the 2-oxo acid dehydrogenase complex. Antimitochondrial autoantibodies (AMA) against OGDC-E2 included immunoglobulin (Ig)G2, IgG3 and IgM and the relative titers were as follows: IgG2 > IgG3 > IgM. Finally, using overlapping recombinant polypeptides, it was determined that a minimum of 81 amino acids (residues 67-147) corresponding to the lipoyl domain of OGDC-E2 are necessary for reactivity, suggesting that a conformational autoepitope is recognized by AMA. These data suggest that each of the 2-oxo acid dehydrogenase enzymes has distinct antigenicity despite their similarities in structure and function. The availability of recombinant OGDC-E2 autoantigen will allow the design of additional studies to further our understanding of the role of mitochondrial autoantigens in the pathogenesis of PBC. (Hepatology 1996 Mar;23(3):436-44)

Pretranslational regulation of pyruvate dehydrogenase complex subunits in white adipose tissue during the suckling-weaning transition in the rat.

Total pyruvate dehydrogenase complex activity is low in white adipose tissue during the suckling period and increases markedly at weaning on to a high-carbohydrate diet. This is concomitant with an increase in the E1 alpha, E1 beta and E2 subunit protein concentration and their respective mRNAs, suggesting a pretranslational control of this phenomenon. The most marked change is seen for the E1 alpha subunit (17-fold increase in protein concentration). The changes in pyruvate dehydrogenase complex activity and subunit abundance induced by weaning on to a high-carbohydrate diet are precluded if the animals are weaned on to a high-fat diet, suggesting that the nutritional and/or related hormonal changes rather than a developmental stage are responsible for the observed adipose-tissue pyruvate dehydrogenase complex pattern.

Immunological comparison of the pyruvate dehydrogenase complexes from pea mitochondria and chloroplasts

The pyruvate dehydrogenase complex (PDC) in pea (Pisum sativum L., cv. Little Marvel) was studied immunologically using antibodies to specific subunits of mammalian PDC. Pea mitochondria and chloroplasts were both found to contain PDC, but distinct differences were noted in the subunit relative molecular mass (Mr) values of the individual enzymes in the mitochondrial and chloroplast PDC complexes. In particular, the mitochondrial E3 enzyme (dihydrolipoamide dehydrogenase; EC 1.8.1.4) has a high subunit Mr value of 67 000, while the chloroplast E3 enzyme has a subunit Mr value of 52 000, similar in size to the prokaryotic, yeast ad mammalian E3 enzymes. In addition, component X (not previously noted in plant PDC) was also found to be present in two distinct forms in pea mitochondrial and chloroplast complexes. As in the case of E3, mitochondrial component X has a higher subunit Mr value (67 000) than component X from chloroplasts (48 000), which is similar in size to its mammalian counterpart. The subunit Mr value of E2 (dihydrolipoamide acetyltransferase; EC 2.3.1.12) in both mitochondria and chloroplasts (50 000) is lower than that of mammalian E2 (74 000) but similar to that of yeast E2 (58 000), and is consistent with the presence of only a single lipoyl domain. Neither mitochondria nor chloroplasts showed any appreciable cross-reactivity with antiserum to mammalian E1 (pyruvate dehydrogenase; EC 1.2.4.1). However, mitochondria cross-reacted strongly with antiserum to yeast E1, giving a single band (Mr 41 000) which is thought to be E1a. Chloroplasts showed no cross-reactivity with yeast E1, indicating that the mitochondrial E1a subunit and its chloroplast equivalent are antigenically distinct polypeptides.

Distribution of dihydrolipoamide acetyltransferase (E2) in the liver and portal lymph nodes of patients with primary biliary cirrhosis: An immunohistochemical study

The reason for the close association between primary biliary cirrhosis and the appearance of antibodies that recognize the E2 component of pyruvate dehydrogenase complex is not understood. The distribution of the three pyruvate dehydrogenase complex subunits was examined in the liver and lymph nodes of patients with primary biliary cirrhosis, patients with other liver diseases and normal subjects by immunohistochemistry using affinity-purified antibodies. Intensity of staining was assessed semiquantitatively and validated by scanning laser confocal microscopy. In primary biliary cirrhosis tissue, the E2 staining pattern did not parallel the reported distribution of mitochondria. E2 staining in biliary epithelial cells was consistently stronger than in hepatocytes. In primary biliary cirrhotic liver, staining of biliary epithelium was significantly stronger than in normal or other liver disease controls; many bile ducts in primary biliary cirrhotic liver demonstrated very high intensity, diffuse distribution of stain. No differences in staining intensity were seen between perivenular hepatocytes in primary biliary cirrhotic liver and those in controls; periportal hepatocytes in primary biliary cirrhotic liver were, however, more intensely stained than perivenular cells. In primary biliary cirrhotic portal lymph nodes, a subset of macrophages showed highintensity, diffuse distribution of stain. By contrast, staining with antibodies to E1 and E3 (other components of pyruvate dehydrogenase complex) produced uniform-intensity, mitochondrial distribution both in primary biliary cirrhosis and control tissue. The increased intensity of E2 in primary biliary cirrhotic tissue could be explained in terms of abnormal metabolism of E2 by biliary epithelial cells. Release of E2 during biliary-tract damage and drainage through the lymphatics could result in uptake by macrophages and the presentation of antigen to lymphocytes in portal lymph nodes.

Distribution of dihydrolipoamide acetyltransferase (E2) in the liver and portal lymph nodes of patients with primary biliary cirrhosis: An immunohistochemical study

The reason for the close association between primary biliary cirrhosis and the appearance of antibodies that recognize the E2 component of pyruvate dehydrogenase complex is not understood. The distribution of the three pyruvate dehydrogenase complex subunits was examined in the liver and lymph nodes of patients with primary biliary cirrhosis, patients with other liver diseases and normal subjects by immunohistochemistry using affinity-purified antibodies. Intensity of staining was assessed semiquantitatively and validated by scanning laser confocal microscopy. In primary biliary cirrhosis tissue, the E2 staining pattern did not parallel the reported distribution of mitochondria. E2 staining in biliary epithelial cells was consistently stronger than in hepatocytes. In primary biliary cirrhotic liver, staining of biliary epithelium was significantly stronger than in normal or other liver disease controls; many bile ducts in primary biliary cirrhotic liver demonstrated very high intensity, diffuse distribution of stain. No differences in staining intensity were seen between perivenular hepatocytes in primary biliary cirrhotic liver and those in controls; periportal hepatocytes in primary biliary cirrhotic liver were, however, more intensely stained than perivenular cells. In primary biliary cirrhotic portal lymph nodes, a subset of macrophages showed high-intensity, diffuse distribution of stain. By contrast, staining with antibodies to E1 and E3 (other components of pyruvate dehydrogenase complex) produced uniform-intensity, mitochondrial distribution both in primary biliary cirrhosis and control tissue. The increased intensity of E2 in primary biliary cirrhotic tissue could be explained in terms of abnormal metabolism of E2 by biliary epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation, characterization and chromosomal localization of cDNA clones for the E1beta subunit of the pyruvate dehydrogenase complex

A full-length cDNA clone for the E1 beta subunit of the human pyruvate dehydrogenase (PyrDH) complex was isolated from a human skin fibroblast cDNA library. When sequenced, it showed differences from the nucleotide sequence already published [Koike, K., Ohta, S., Urata, Y., Kagawa, Y. & Koike, M. (1988) Proc. Natl Acad. Sci. USA 85, 41-45], such that 19 amino acids were different in the translated open reading frame. Northern blotting of human fibroblast cell lines revealed a major mRNA species of 1.6 kb and a weaker band of 5.5 kb. In a series of nine PyrDH-complex-deficient cell lines from patients with this deficiency, no patients had severely reduced amounts of mRNA, but there was one patient cell line with an increased amount of abnormal-size mRNA. Chromosome localization carried out with DNA blots from man-mouse hybrid cell lines indicated that the E1 beta subunit of pyruvate dehydrogenase is located on chromosome 3. A motif AXGXXXXGL(R/K)X15(D/E)Q was found in common with a variety of other oxo-acid oxidoreductases, but its function is not known.

Biosynthesis, import and processing of precursor polypeptides of mammalian mitochondrial pyruvate dehydrogenase complex.

An immunological analysis has been conducted of early events in the biosynthesis, import and assembly of the mammalian pyruvate dehydrogenase complex (PDC). For this purpose, monospecific polyclonal antisera were produced against the intact assembly from ox heart, Mr 8.5 x 10(6), and each of its component polypeptides, E1 alpha, E1 beta, E2, E3 and protein X. Optimal detergent-based incubation mixtures were developed for obtaining clean immunoprecipitation of PDC polypeptides and their precursors from [35S]methionine-labelled extracts of PK-15 (pig kidney), NBL-1 (bovine kidney) and BRL (Buffalo Rat liver) cells. In PK-15 cells, independent higher Mr species, corresponding to precursors of the E2, E1 alpha and E1 beta subunits of PDC, could be detected by immune precipitation and fluorography after incubation of intact cells for 4 h with [35S]methionine and 1-2 mM-2,4-dinitrophenol or 10-15 microM-carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Similar precursor states could be observed in uncoupler-treated BRL or NBL-1 cells. Pre-E1 alpha, pre-E1 beta and also pre-E3, have signal sequences in the Mr range 1500-3000 while pre-E2 contains a long additional segment of Mr 7000-9000. All of these forms exhibit similar kinetics of processing to the mature subunits with a transit time of 10-12 min. In NBL-1 cells, E3 is present in the immune complexes formed with anti-PDC serum whereas this is not the case in PK-15 cells. Thus, there are significant variations in the affinity of lipoamide dehydrogenase (E3) for the E2 core structure in different species. Pre-E1 alpha accumulates only poorly in PK-15 cells and is aberrantly processed on removal of uncoupler. This precursor is markedly more stable in NBL-1 and BRL cells. The lack of detection of a precursor form of component X is also discussed.

Isolation of a full-length complementary DNA coding for human E1 alpha subunit of the pyruvate dehydrogenase complex.

A 1.5-kilobase cDNA clone for human pyruvate dehydrogenase E1 was isolated from a lambda gt11 expression library by screening with polyclonal antiserum to the E1 alpha subunit of the porcine pyruvate dehydrogenase complex, a polyclonal antibody against bovine pyruvate dehydrogenase complex and a synthetic oligonucleotide based on the known amino acid sequence of the amino-terminal of the bovine pyruvate dehydrogenase-E1 alpha subunit. Nucleotide sequence analysis of the cDNA revealed a 5'-untranslated sequence of 72 nucleotides, a translated sequence of 1170 nucleotides, and a 3'-untranslated sequence of 223 nucleotides with a poly(A) tail. The cDNA structure predicts a leader sequence of 29 amino acids and a mature protein of 362 amino acids comprising an amino-terminal peptide identical to that of the bovine E1 alpha subunit and three serine phosphorylation sites whose sequence was also identical to those in the bovine E1 alpha subunit. The translated sequence for the mature protein differs substantially from that described by Dahl et al. (Dahl, H. H., Hunt, S. M., Hutchison, W. M., and Brown, G. K. (1987) J. Biol. Chem. 262, 7398-7403) by virtue of a frameslip between bases 390 and 594. This amended sequence is confirmed by the presence of additional restriction sites for the enzymes NaeI and HaeII at the beginning and end, respectively, of this section. The leader sequence is typical for mitochondrial enzymes being composed of a combination of neutral and basic residues. The amino acid composition is strikingly similar to that of the bovine protein. This cDNA clone hybridizes with a 1.8-kilobase mRNA on a Northern blot analysis of human fibroblasts, and a second minor band of 4.4 kilobases is also detected.

Identification of a 42K phosphoprotein of platelets modulated by collagen: The α-subunit of pyruvate dehydrogenase

Platelets exposed to collagen sufficient to stimulate the release reaction show an increase in labeling of two intracellular proteins with molecular weights of 20,000 and 42,000. The 20,000 M r protein has already been identified as the light chain of myosin whereas the identity of the 42,000 M r protein had not been established. By use of biochemical and immunological techniques, the identify of the 42,000 M r component of prelabeled platelets found in the 100,000 g supernatant of freeze-thawed or sonicated cells appears to be one of the subunits of pyruvate dehydrogenase complex which is translocated from the mitochondria to the 100,000 g supernatant during the preparative procedure. Increased phosphorylation of the 42,000 M r protein occurred after collagen stimulation and was accompanied by diminished pyruvate dehydrogenase activity.