Effect of the hinge protein on the heme iron site of cytochrome c1

Cardiac mitochondrial matrix and respiratory complex protein phosphorylation

It has become appreciated over the last several years that protein phosphorylation within the cardiac mitochondrial matrix and respiratory complexes is extensive. Given the importance of oxidative phosphorylation and the balance of energy metabolism in the heart, the potential regulatory effect of these classical signaling events on mitochondrial function is of interest. However, the functional impact of protein phosphorylation and the kinase/phosphatase system responsible for it are relatively unknown. Exceptions include the well-characterized pyruvate dehydrogenase and branched chain α-ketoacid dehydrogenase regulatory system. The first task of this review is to update the current status of protein phosphorylation detection primarily in the matrix and evaluate evidence linking these events with enzymatic function or protein processing. To manage the scope of this effort, we have focused on the pathways involved in energy metabolism. The high sensitivity of modern methods of detecting protein phosphorylation and the low specificity of many kinases suggests that detection of protein phosphorylation sites without information on the mole fraction of phosphorylation is difficult to interpret, especially in metabolic enzymes, and is likely irrelevant to function. However, several systems including protein translocation, adenine nucleotide translocase, cytochrome c, and complex IV protein phosphorylation have been well correlated with enzymatic function along with the classical dehydrogenase systems. The second task is to review the current understanding of the kinase/phosphatase system within the matrix. Though it is clear that protein phosphorylation occurs within the matrix, based on (32)P incorporation and quantitative mass spectrometry measures, the kinase/phosphatase system responsible for this process is ill-defined. An argument is presented that remnants of the much more labile bacterial protein phosphoryl transfer system may be present in the matrix and that the evaluation of this possibility will require the application of approaches developed for bacterial cell signaling to the mitochondria.

UQCRH gene encoding mitochondrial Hinge protein is interrupted by a translocation in a soft-tissue sarcoma and epigenetically inactivated in some cancer cell lines

We previously reported the identification of a novel zinc-finger gene, designated ZSG, fused to Ewing sarcoma gene (EWS) by a submicroscopic paracentric inversion of 22q12 in a small round cell sarcoma presenting a translocation t(1;22)(p34;q12). We report here the molecular cloning and characterization of the breakpoint in 1p34, which encompasses the gene coding for mitochondrial Hinge protein ubiquinol-cytochrome C reductase hinge gene (UQCRH). All the three breakpoints, two on 22q12 and one in 1p34, interrupt different genes: EWS, ZSG and UQCRH. We determined the genomic structure of UQCRH, characterized its splicing variants and identified a transcribed processed pseudogene. The analysis of UQCRH expression in normal tissues and cancer cell lines revealed absent expression of UQCRH in two ovarian and one breast cancer cell lines and reduced expression in a further breast carcinoma cell line. CpG island methylation upstream exon 1 was detected in all the three cell lines with absent expression. Moreover, treatment with demethylating agent 5-azacytidine restored UQCRH expression in OAW42 ovarian cancer cells. These data provide preliminary evidence of the inactivation of UQCRH gene in cancer either by structural rearrangements or epigenetic mechanisms.