Pyruvate Dehydrogenase E1 Subunit Research Articles

Assessing the Thiamine Diphosphate Dependent Pyruvate Dehydrogenase E1 Subunit for Carboligation Reactions with Aliphatic Ketoacids.

The synthetic properties of the Thiamine diphosphate (ThDP)-dependent pyruvate dehydrogenase E1 subunit from Escherichia coli (EcPDH E1) was assessed for carboligation reactions with aliphatic ketoacids. Due to its role in metabolism, EcPDH E1 was previously characterised with respect to its biochemical properties, but it was never applied for synthetic purposes. Here, we show that EcPDH E1 is a promising biocatalyst for the production of chiral α-hydroxyketones. WT EcPDH E1 shows a 180–250-fold higher catalytic efficiency towards 2-oxobutyrate or pyruvate, respectively, in comparison to engineered transketolase variants from Geobacillus stearothermophilus (TKGST). Its broad active site cleft allows for the efficient conversion of both (R)- and (S)-configured α-hydroxyaldehydes, next to linear and branched aliphatic aldehydes as acceptor substrates under kinetically controlled conditions. The alternate, thermodynamically controlled self-reaction of aliphatic aldehydes was shown to be limited to low levels of conversion, which we propose to be due to their large hydration constants. Additionally, the thermodynamically controlled approach was demonstrated to suffer from a loss of stereoselectivity, which makes it unfeasible for aliphatic substrates.

LncRNA MEG3 promotes endoplasmic reticulum stress and suppresses proliferation and invasion of colorectal carcinoma cells through the MEG3/miR-103a-3p/PDHB ceRNA pathway.

LncRNA maternally expressed gene 3 (MEG3) is a potential prognostic and diagnostic biomarker in colorectal carcinoma (CC). However, its cellular functions and mechanism remain not fully uncovered. Relative expression of MEG3, miRNA (miR)-103a-3p, and pyruvate dehydrogenase E1 subunit beta (PDHB) was detected by RT-qPCR and western blotting. Cell proliferation was measured by CCK-8 assay, colony formation assay, and flow cytometry, as well as xenograft tumor assay. Transwell assay examined cell invasion. Endoplasmic reticulum (ER) stress was evaluated by western blotting. Dual-luciferase reporter assay and RNA immunoprecipitation determined the relationship between miR-103a-3p and MEG3 or PDHB. Expression of MEG3 was downregulated in human CC tumor tissues and cells (SW620 and HCT116), accompanied by higher miR-103a-3p and lower PDHB. Restoring MEG3 suppressed cell viability, colony formation ability, and invasion, arrested cell cycle, and induced apoptosis rate in SW620 and HCT116 cells, as well as promoted expression of ER stress-related proteins (GRP78, ATF6, CHOP, caspase-3, and caspase-9). Furthermore, MEG3 overexpression hindered tumor growth and facilitated ER stress in vivo. Molecularly, miR-103a-3p was a target of MEG3, and further targeted PDHB. Similarly, in function, blocking miR-103a-3p suppressed CC in vitro by affecting proliferation, invasion, and ER stress; in addition, restoring miR-103a-3p partially counteracted the suppressive role of MEG3 in CC cells. MEG3 sponged miR-103a-3p to suppress CC malignancy by inducing ER stress and inhibiting cell proliferation and invasion via upregulating PDHB, suggesting a novel MEG3/miR-103a-3p/PDHB ceRNA pathway.

Diagnosis of human and canine Brucella canis infection: development and evaluation of indirect enzyme-linked immunosorbent assays using recombinant Brucella proteins

Brucella canis, a Gram-negative coccobacilli belonging to the genus Brucellae, is a pathogenic bacterium that can produce infections in dogs and humans. Multiple studies have been carried out to develop diagnostic techniques to detect all zoonotic Brucellae. Diagnosis of Brucella canis infection is challenging due to the lack of highly specific and sensitive diagnostic assays. This work was divided in two phases: in the first one, were identified antigenic proteins in B. canis that could potentially be used for serological diagnosis of brucellosis. Human sera positive for canine brucellosis infection was used to recognize immunoreactive proteins that were then identified by performing 2D-GEL and immunoblot assays. These spots were analyzed using MALDI TOF MS and predicted proteins were identified. Of the 35 protein spots analyzed, 14 proteins were identified and subsequently characterized using bioinformatics, two of this were selected for the next phase. In the second phase, we developed and validated an indirect enzyme-linked immunosorbent assays using those recombinant proteins: inosine 5′ phosphate dehydrogenase, pyruvate dehydrogenase E1 subunit beta (PdhB) and elongation factor Tu (Tuf). These genes were PCR-amplified from genomic DNA of B. canis strain Oliveri, cloned, and expressed in Escherichia coli. Recombinant proteins were purified by metal affinity chromatography, and used as antigens in indirect ELISA. Serum samples from healthy and B. canis-infected humans and dogs were used to evaluate the performance of indirect ELISAs. Our results suggest that PdhB and Tuf proteins could be used as antigens for serologic detection of B. canis infection in humans, but not in dogs. The use of recombinant antigens in iELISA assays to detect B. canis-specific antibodies in human serum could be a valuable tool to improve diagnosis of human brucellosis caused by B. canis.

Identification of immunogenic proteins and evaluation of recombinant PDHA1 and GAPDH as potential vaccine candidates against Streptococcus iniae infection in flounder (Paralichthys olivaceus).

Streptococcus iniae is a major Gram-positive pathogen that causes invasive disease in fish worldwide. In this study, in order to identify immunogenic proteins for developing highly effective vaccine against S. iniae, whole-cell lysate proteins of S. iniae were analyzed by western blotting using flounder anti-S. iniae antibodies, and two positive protein bands of molecular weight 37 kDa and 40 kDa were screened, which were identified as pyruvate dehydrogenase E1 subunit alpha (PDHA1), BMP family ABC transporter substrate-binding protein (BMP) and L-lactate dehydrogenase (LDH), as well as ornithine carbamoyltransferase (OCT), lactate oxidas (LOx) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by mass spectrometry. Subsequently, the six recombinant proteins were produced and used to immunize healthy flounder, and the relative percent survival (RPS) value was 72.73%, 27.27%, 36.36%, 9.09%, 36.36% and 63.64% respectively after intraperitoneal challenge with live S. iniae, revealing that rPDHA1 and rGAPDH produced higher relative percent survival than formalin-killed S. iniae (36.36%). To further investigate the protective efficacy of rPDHA1 and rGAPDH, the proliferation of surface membrane immunoglobulin-positive (sIg+) lymphocytes in peripheral blood leucocytes, the total serum IgM, specific IgM against S. iniae and RPS were detected. The results showed that rPDHA1, rGAPDH and formalin-killed S. iniae significantly induced the proliferation of sIg+ lymphocytes, the production of total serum IgM and specific IgM as compared with the control group, and rGAPDH and rPDHA1 provide higher RPS (62.5% and 75%, respectively) again. These results demonstrated that rPDHA1 and rGAPDH are promising vaccine candidates against S. iniae infection in flounder.

Development of multilocus putatively neutral DNA markers in the X-chromosome for population genetic studies in humans

Background: It has now been well documented that the type (coding, non-coding) and location (nuclear, mitochondrial etc.) of genetic markers heavily influence evolutionary inferences; realistic assumptions can be drawn if multiple putatively neutral DNA fragments spread across the genome are used.Aim: To infer human population history, Single Nucleotide Polymorphisms (SNPs), located in the non-coding regions of different genes in the X-chromosome have been developed as ‘putatively neutral markers’.Subjects and methods: A population sample consisting of 16 male individuals from the western part of India was utilized for sequencing eight DNA fragments located in introns of three genes (Duchenne muscular dystrophy, Factor IX and Pyruvate dehydrogenase E1 sub-unit) on the human X-chromosome. PCR amplification and DNA sequencing confirmed the polymorphic status of all the fragments.Results: Twenty nine SNPs were found to be segregating in the Western Indian population samples. Using these SNPs the nucleotide diversity and demographic parameters of the Western Indian population were estimated. Several tests of neutrality ascertained that all eight fragments evolve putatively neutrally. Further, linkage disequilibrium analyses confirmed this fact.Conclusion: All eight DNA fragments seem to bear the characteristics to be considered as ‘putatively neutral genetic markers’ and thus, could be utilized for inference of human population and demographic histories.

Myocardial oxidative stress, osteogenic phenotype, and energy metabolism are differentially involved in the initiation and early progression of δ-sarcoglycan-null cardiomyopathy

Dilated cardiomyopathy (DCM) is a common cause of heart failure, and identification of early pathogenic events occurring prior to the onset of cardiac dysfunction is of mechanistic, diagnostic, and therapeutic importance. The work characterized early biochemical pathogenesis in TO2 strain hamsters lacking delta-sarcoglycan. Although the TO2 hamster heart exhibits normal function at 1 month of age (presymptomatic stage), elevated levels of myeloperoxidase, monocyte chemotactic protein-1, malondialdehyde, osteopontin, and alkaline phosphatase were evident, indicating the presence of inflammation, oxidative stress, and osteogenic phenotype. These changes were localized primarily to the myocardium. Derangement in energy metabolism was identified at the symptomatic stage (4 month), and is marked by attenuated activity and expression of pyruvate dehydrogenase E1 subunit, which catalyzes the rate-limiting step in aerobic glucose metabolism. Thus, this study illustrates differential involvement of oxidative stress, osteogenic phenotype, and glucose metabolism in the initiation and early progression of delta-sarcoglycan-null DCM.

Identification of the Loci of Interaction between the E1 and E2 Subunits of the Pyruvate Dehydrogenase Complex from Escherichia coli

Earlier, we reported that residues 1–45 of Escherichia coli pyruvate dehydrogenase E1 subunit interact with the second E2 subunit (Park et al., 2004 Biochemistry). Substitution of the highly conserved E1 residues, D7, D9, P10, I11, E12, T13, R14, and D15 by A, D or N, identified D7, D9, E12, R14, and D15 to be involved in E1–E2 interactions. We report charge-reversed substitutions at D9, E12, E21, E26, E27, E30, D37, and E42 to arginine. Also, the highly conserved residues on E2, R129 and R150 were found to bind to E1. Apparently, the positively charged residues on the subunit-binding domain of E2 interact with the negatively charged N-terminal residues on E1. While the E21R, E26R, D37R, and E42R E1 variants could form a complex with E2 and produce NADH in the overall assay, the D9R, E12R, E27R and E30R variants led to weakened interaction with PDHc-E2 in both respects. The folding ability of E1 was especially affected by the E30R substitution. According to MALDI-MS, the D9R E1 substitution did not impair its ability to reductively acetylate independently expressed lipoyl domain. Apparently, D9, E12, E27, and E30 on E1 have a role in binding E2, not in decarboxylating pyruvate. Supported by NIH GM-050380.

Crystal Structure of 1-Deoxy-d-xylulose 5-Phosphate Synthase, a Crucial Enzyme for Isoprenoids Biosynthesis

Isopentenyl pyrophosphate (IPP) is a common precursor for the synthesis of all isoprenoids, which have important functions in living organisms. IPP is produced by the mevalonate pathway in archaea, fungi, and animals. In contrast, IPP is synthesized by a mevalonate-independent pathway in most bacteria, algae, and plant plastids. 1-Deoxy-D-xylulose 5-phosphate synthase (DXS) catalyzes the first and the rate-limiting step of the mevalonate-independent pathway and is an attractive target for the development of novel antibiotics, antimalarials, and herbicides. We report here the first structural information on DXS, from Escherichia coli and Deinococcus radiodurans, in complex with the coenzyme thiamine pyrophosphate (TPP). The structure contains three domains (I, II, and III), each of which bears homology to the equivalent domains in transketolase and the E1 subunit of pyruvate dehydrogenase. However, DXS has a novel arrangement of these domains as compared with the other enzymes, such that the active site of DXS is located at the interface of domains I and II in the same monomer, whereas that of transketolase is located at the interface of the dimer. The coenzyme TPP is mostly buried in the complex, but the C-2 atom of its thiazolium ring is exposed to a pocket that is the substrate-binding site. The structures identify residues that may have important roles in catalysis, which have been confirmed by our mutagenesis studies.

Pirin Regulates Pyruvate Catabolism by Interacting with the Pyruvate Dehydrogenase E1 Subunit and Modulating Pyruvate Dehydrogenase Activity

The protein pirin, which is involved in a variety of biological processes, is conserved from prokaryotic microorganisms, fungi, and plants to mammals. It acts as a transcriptional cofactor or an apoptosis-related protein in mammals and is involved in seed germination and seedling development in plants. In prokaryotes, while pirin is stress induced in cyanobacteria and may act as a quercetinase in Escherichia coli, the functions of pirin orthologs remain mostly uncharacterized. We show that the Serratia marcescens pirin (pirin(Sm)) gene encodes an ortholog of pirin protein. Protein pull-down and bacterial two-hybrid assays followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrospray ionization-tandem mass spectrometry analyses showed the pyruvate dehydrogenase (PDH) E1 subunit as a component interacting with the pirin(Sm) gene. Functional analyses showed that both PDH E1 subunit activity and PDH enzyme complex activity are inhibited by the pirin(Sm) gene in S. marcescens CH-1. The S. marcescens CH-1 pirin(Sm) gene was subsequently mutated by insertion-deletion homologous recombination. Accordingly, the PDH E1 and PDH enzyme complex activities and cellular ATP concentration increased up to 250%, 140%, and 220%, respectively, in the S. marcescens CH-1 pirin(Sm) mutant. Concomitantly, the cellular NADH/NAD(+) ratio increased in the pirin(Sm) mutant, indicating increased tricarboxylic acid (TCA) cycle activity. Our results show that the pirin(Sm) gene plays a regulatory role in the process of pyruvate catabolism to acetyl coenzyme A through interaction with the PDH E1 subunit and inhibiting PDH enzyme complex activity in S. marcescens CH-1, and they suggest that pirin(Sm) is an important protein involved in determining the direction of pyruvate metabolism towards either the TCA cycle or the fermentation pathways.

A Thiamin-bound, Pre-decarboxylation Reaction Intermediate Analogue in the Pyruvate Dehydrogenase E1 Subunit Induces Large Scale Disorder-to-Order Transformations in the Enzyme and Reveals Novel Structural Features in the Covalently Bound Adduct

The crystal structure of the E1 component from the Escherichia coli pyruvate dehydrogenase multienzyme complex (PDHc) has been determined with phosphonolactylthiamin diphosphate (PLThDP) in its active site. PLThDP serves as a structural and electrostatic analogue of the natural intermediate alpha-lactylthiamin diphosphate (LThDP), in which the carboxylate from the natural substrate pyruvate is replaced by a phosphonate group. This represents the first example of an experimentally determined, three-dimensional structure of a thiamin diphosphate (ThDP)-dependent enzyme containing a covalently bound, pre-decarboxylation reaction intermediate analogue and should serve as a model for the corresponding intermediates in other ThDP-dependent decarboxylases. Regarding the PDHc-specific reaction, the presence of PLThDP induces large scale conformational changes in the enzyme. In conjunction with the E1-PLThDP and E1-ThDP structures, analysis of a H407A E1-PLThDP variant structure shows that an interaction between His-407 and PLThDP is essential for stabilization of two loop regions in the active site that are otherwise disordered in the absence of intermediate analogue. This ordering completes formation of the active site and creates a new ordered surface likely involved in interactions with the lipoyl domains of E2s within the PDHc complex. The tetrahedral intermediate analogue is tightly held in the active site through direct hydrogen bonds to residues His-407, Tyr-599, and His-640 and reveals a new, enzyme-induced, strain-related feature that appears to aid in the decarboxylation process. This feature is almost certainly present in all ThDP-dependent decarboxylases; thus its inclusion in our understanding of general thiamin catalysis is important.

Females with PDHA1 gene mutations: A diagnostic challenge

Biochemical analysis was performed in muscle tissue and in fibroblasts of four unrelated females consecutively diagnosed with a ‘de novo’ point mutation in the PDHA1 gene. Pyruvate dehydrogenase E1 subunit deficiency was confirmed in the muscle sample of all patients, however, in three out of four cases the activity of the pyruvate dehydrogenase complex in fibroblasts showed a normal activity. A skewed inactivation was confirmed of the maternal X chromosome in fibroblasts in all children. Due to the possibility of a skewed X inactivation pattern enzyme measurements in fibroblasts are not always reliable for the diagnosis of a PDHc defect in females. Based on the overlapping features of PDHc deficiency with those of the disorders of the oxidative phosphorylation we suggest performing a fresh muscle biopsy for detailed biochemical analysis in females with a suspected pyruvate dehydrogenase deficiency, followed by molecular genetic analysis of the PDHA1 gene.

Construction of a cysteineless variant of the E. coli pyruvate dehydrogenase E1 subunit

The crystal structure of the E1 subunit of the pyruvate dehydrogenase complex from E. coli (PDHc-E1) revealed three regions of low electron density, spanning residues 1–55, 401–413 and 541–557 (Arjunan et al., Biochemistry 2002, 41, 5213–5221). Region 1–55 has been shown to interact with the PDHc-E2 subunit (Park et al, Biochemistry 2004, 43, 14037–14046) while region 401–413 has a role in reductive acetylation of the lipoamide of the PDHc-E2 subunit (Nemeria et al., Biochemistry 2002, 41, 15459–15467). Studies using site specific labeling (SSL) with thiol-directed probes sensitive to their local environment has immense potential to characterize the dynamics of these important regions. For this purpose five of six cysteine residues in parental PDHc-E1 (120, 259, 575, 610, 654 and 770) were converted to alanines, the sixth C259 to asparagine, by site directed mutagenesis. This PDHc-E1 variant without cysteines showed ~4-fold reduction in activity compared to parental PDHc-E1 in subunit-specific as well as overall complex activity assays. These results confirm our previous observations (Nemeria et al, Biochemistry 1998, 37, 911–922) where none of the cysteines in singly-substituted PDHc-E1 were found important for activity. Moreover, reintroduction of cysteine for SSL studies in regions 1–55 (I11C) and 401–413 (Q408C) did not result in significant reduction in PDHc-E1 activity, retaining ~40% and 80% overall activity, respectively, compared to the cysteineless PDHc-E1 variant. These results will facilitate SSL and functional characterization of these important regions in PDHc-E1. Supported by NIH grants GM62330 and GM53080.

A mutant pyruvate dehydrogenase E1 subunit allows survival of Escherichia coli strains defective in 1-deoxy-d-xylulose 5-phosphate synthase

The 2-C-methyl-d-erythritol 4-phosphate pathway has been proposed as a promising target to develop new antimicrobial agents. However, spontaneous mutations in Escherichia coli were observed to rescue the otherwise lethal loss of the first two enzymes of the pathway, 1-deoxy-d-xylulose 5-phosphate (DXP) synthase (DXS) and DXP reductoisomerase (DXR), with a relatively high frequency. A mutation in the gene encoding the E1 subunit of the pyruvate dehydrogenase complex was shown to be sufficient to rescue the lack of DXS but not DXR in vivo, suggesting that the mutant enzyme likely allows the synthesis of DXP or an alternative substrate for DXR.

Studies on thiamine diphosphate-dependent enzymes

The 3-deaza analogue of TPP (thiamine diphosphate), a close mimic of the ylid intermediate, has been synthesized and is an extremely potent inhibitor of a variety of TPP-dependent enzymes, binding much more tightly than TPP itself. Results using deazaTPP complexed with the E1 subunit of PDH (pyruvate dehydrogenase) have led to a novel proposal about the mechanism of this enzyme. The 2-substituted forms of deazaTPP, which mimic other intermediates in the catalytic mechanism, can also be synthesized and 2-(1-hydroxyethyl)deazaTPP is also an extremely potent inhibitor of PDC (pyruvate decarboxylase). Attachment of such 2-substituents is expected to be a way to introduce selectivity in the inhibition of various TPP-dependent enzymes.

Pyruvate dehydrogenase E1 α isoform in rat testis: cDNA cloning, characterization, and biochemical comparison of the recombinant testis and liver enzymes

Previous data indicated a tissue-specific regulation of mitochondrial pyruvate dehydrogenase (PDH) complex, especially in the brain and testis. The lack of biochemical data on the rat testis PDH limits comparative analysis between testis and liver enzymes. Therefore, we have isolated a cDNA clone encoding rat testis PDH E1 α isoform, determined its nucleotide sequence, studied the tissue-specific expression, and characterized the recombinant protein produced in bacteria, compared to the liver counterpart. Our cDNA clone (2.2 kb) contained the identical open reading frame (from nt 974 to 2149) with that previously reported (Cullingford et al., 1993 Biochim Biophys Acta 1216:149–153) but contained a long 5′ untranslated region, which has little identity to the other clone. Northern blot confirmed testis-specific expression of this isoform. Genomic DNA analyses by PCR amplification suggested this clone is a gene product distinct from its X-linked somatic counterpart. Our biochemical and kinetic analyses revealed that the purified recombinant rat testis PDH E1 (containing both E1 α and E1 β subunits) was enzymatically active and phosphorylated in vitro by purified PDH-kinase p48 or p45, similar to the recombinant human liver enzyme. Our current data thus indicate that the differential regulation of testis PDH observed in the animal model may result from differential modulation of PDH-kinase or -phosphatase in this tissue rather than the presence of functionally different PDH E1 subunit.

Identification of a thiamin-dependent synthase in Escherichia coli required for the formation of the 1-deoxy-D-xylulose 5-phosphate precursor to isoprenoids, thiamin, and pyridoxol.

In Escherichia coli, 1-deoxy-D-xylulose (or its 5-phosphate, DXP) is the biosynthetic precursor to isopentenyl diphosphate [Broers, S. T. J. (1994) Dissertation (Eidgenössische Technische Hochschule, Zürich)], thiamin, and pyridoxol [Himmeldirk, K., Kennedy, I. A., Hill, R. E., Sayer, B. G. & Spenser, I. D. (1996) Chem. Commun. 1187-1188]. Here we show that an open reading frame at 9 min on the chromosomal map of E. coli encodes an enzyme (deoxyxylulose-5-phosphate synthase, DXP synthase) that catalyzes a thiamin diphosphate-dependent acyloin condensation reaction between C atoms 2 and 3 of pyruvate and glyceraldehyde 3-phosphate to yield DXP. We have cloned and overexpressed the gene (dxs), and the enzyme was purified 17-fold to a specific activity of 0.85 unit/mg of protein. The reaction catalyzed by DXP synthase yielded exclusively DXP, which was characterized by 1H and 31P NMR spectroscopy. Although DXP synthase of E. coli shows sequence similarity to both transketolases and the E1 subunit of pyruvate dehydrogenase, it is a member of a distinct protein family, and putative DXP synthase sequences appear to be widespread in bacteria and plant chloroplasts.

Yeast TKL1 gene encodes a transketolase that is required for efficient glycolysis and biosynthesis of aromatic amino acids.

A gene encoding transketolase, TKL1, was cloned from the budding yeast Saccharomyces cerevisiae using oligonucleotide primers derived from protein sequence data. The TKL1 sequence predicts a 74-kDa polypeptide which is related to other transketolases. A sequence comparison revealed that the transketolases can be subdivided into three evolutionary branches. We also found that the transketolases are related to another vitamin B1-dependent enzyme: the E1 subunit of pyruvate dehydrogenase from Escherichia coli. Gene disruption and overexpression experiments were used to investigate the function of transketolase in yeast. We found that growth on fermentable carbon sources, but not on gluconeogenic carbon sources, is reduced in cells disrupted for TKL1. This suggests that the glycolytic efficiency is impaired. Growth on fermentable carbon sources is also reduced in cells that overexpress TKL1. Finally, we found that cells disrupted for TKL1 are unable to grow in the absence of aromatic amino acids. This is most likely due to the fact that transketolase is required for the synthesis of erythrose-4-P, a precursor of the aromatic amino acids.

Pyruvate dehydrogenase (PDH) deficiency caused by a 21-base pair insertion mutation in the Elα subunit

We report the molecular characterization of a case of a functional PDH-E1 (E1 subunit of pyruvate dehydrogenase) deficiency, a cause of severe congenital lactic acidosis. Residual PDH-E1 activity was reduced to 10% of normal values, although the subunit appeared to be quantitatively and qualitatively normal at the protein level as determined by Western blotting. The sequence of PDH-E1 alpha mRNA and the corresponding genomic DNA revealed an in-frame 21-bp insertion between codons 305 and 306 of the normal E1 alpha cDNA. The mutational insert commences with a novel GAT codon and is a nearly perfect tandem duplication of the wild type DNA sequence. A serine phosphorylation site regulating the activity of the PDH complex is altered by this insertion, which in all likelihood is responsible for the functional enzymatic deficiency leading to lactic acidosis.

Pyruvate decarboxylase is like acetolactate synthase ( ILV2) and not like the pyruvate dehydrogenase E1 subunit

Protein sequences of pyruvate decarboxylase (PDC) derived from cloned yeast ( Saccharomyces cerevisiae) and bacterial ( Zymomonas mobilis) genes were compared with each other and with sequence databases. Extensive sequence similarities were found between them and with two others: cytochrome-linked pyruvate oxidase from Escherichia coli and acetolactate synthase ( ilvI in E. coli; ILV2 gene in S. cerevisiae). All catalyse decarboxylation of pyruvate using thiamine pyrophosphate (TPP) as cofactor. General overall similarity suggests common ancestry for these enzymes. None of the sequences was similar to the E1 component of pyruvate dehydrogenase from E. coli which also decarboxylates pyruvate with the help of TPP.