Role of the regulatory subunit of bovine pyruvate dehydrogenase phosphatase.

Abstract

Bovine pyruvate dehydrogenase phosphatase (PDP) is a Mg2+-dependent and Ca2+-stimulated heterodimer that is a member of the protein phosphatase 2C family and is localized to mitochondria. Insight into the function of the regulatory subunit of PDP (PDPr) has been gained. It Both phosphorylated El (P-E1) and PDP must be bound to the 60-mer icosahedral dihydrolipoamide acetyltransferase (E2) component of PDC to obtain a maximum rate of dephosphorylation. Ca>2 apparently mediates the specific binding of PDP to E2 in juxtaposition to P-El (7). This orientation decreases the apparent Km of PDP for P-El (7) and for Mg2> (6). There appears to be two Ca2+-binding sites, one intrinsic to PDPc and a second produced by association of PDP with E2 (2).At subsaturating concentrations of Mg2>, PDP activity is stimulated by polyamines, particularly spermine (8). Like Ca2+, spermine decreases the apparent Km of PDP for Mg2+ but by a different but hitherto unknown mechanism (6,8,9). This paper reports that PDPr decreases the sensitivity of PDPc to Mg2+ and that this effect is reversed by spermine, which apparently interacts with PDPr. These observations are potentially significant in understanding the molecular basis of the insulin-induced activation of the mitochondrial PDP.MATERIALS AND METHODS Materials. Highly purified PDC and PDP were prepared from bovine kidney mitochondria (10, 11). Recombinant PDPc was expressed in Escherichia coli and purified to near homogeneity (3). EB and E2 were obtained by resolution of the PDC (11). The E2 contained small amounts of tightly bound E3-binding protein (protein X) and PDH kinase (E2-X-K complex). The peptides RRASVA and RRATVA were prepared manually by solid-phase synthesis using Boc-Ala-Pam resin and Boc-protected amino acids (Peptides International 32P-labeled P-El was prepared by incubating a solution containing 10 mg of E1, 50 ,ug of E2-X-K complex, and 0.1 mM [,y-32P]ATP in 2 ml of buffer A for 1 h at 30°C. The solution was adjusted to pH 5.8 to precipitate P-El, which was dissolved in a small volume of buffer A, the solution was dialyzed against three changes of buffer A, and then centrifuged at 35,000 rpm and 4°C for 1-5 h in a Beckman model Optima TLX ultracentrifuge. The P-El contained 9-12 nmol of phosphate groups per mg of protein. P-El was also prepared by resolution of P-PDC (11).The peptides RRASVA and RRATVA were phosphorylated by incubating for 8-10 h at 30°C a solution containing 10 mg peptide, 25 mM Tris HCl (pH 7.3), 2.5 mM MgCl2, 0.1% 2-mercaptoethanol, 10% glycerol, 0.1 mM [,y-32P]ATP, and 40 units of protein kinase A catalytic subunit in a final volume of 2 ml (12). The reaction was terminated by adding 2 ml of 60% acetic acid, and the solution was passed through an anionexchange column (1.0 x 4 cm) of Dowex 2X8-100 equilibrated with 30% acetic acid. The flowthrough, which contained the phosphopeptide, was lyophilized. The peptide was dissolved in 1 ml of 25 mM Tris-HCl (pH 7.3), 0.1% 2-mercaptoethanol, and the pH was adjusted to 7.3 with 1 M Tris (pH 10...

E4F1 controls a transcriptional program essential for pyruvate dehydrogenase activity

“…These genes encode the E2 and E3 subunits of the PDH core enzyme (Dlat, Dld), the mitochondrial pyruvate transporter MPC1 (Brp44l), and the mitochondrial transporter of the PDH cofactor thiamine pyrophosphate (Slc25a19/DNC). A fifth gene, encoding the negative regulator of the PDH phosphatases (Pdpr) (27) was also identified as an E4F1 target gene by ChIP-seq in transformed fibroblasts, but not in ES cells (data not shown). does not bind.…”

Recent advances in mechanisms regulating glucose oxidation at the level of the pyruvate dehydrogenase complex by PDKs

“…The catalytic subunit (PDP1c) is in the phosphatase 2C class (28). The regulatory subunit (PDP1r) is a flavoprotein with a bound flavin adenine dinucleotide that influences the Mg 2ϩ concentration that is required for PDP1c activity (29,69). The second PDP isoform, PDP2, is found in liver and adipose tissue (18).…”

From lipoic acid to multi‐enzyme complexes

“…By comparing the properties of recombinant PDPc and the native PDH phosphatase heterodimer (PDPc bound to PDPr), we obtained insight into the function of PDPr. Jiangong Yan found that PDPr decreases the sensitivity of PDPc to Mg2+ and that spermine increases the sensitivity of PDH phosphatase but not PDPc to Mg2+, apparently by interacting with PDPr (Yan et al, 1996). We interpret these observations to indicate that PDPr blocks or distorts the Mg2+-binding site of PDPc and that spermine produces a conformational change in PDPr (allosteric effect) that reverses its inhibitory effect.…”