The first patient diagnosed with cytochrome c oxidase deficient Leigh syndrome: progress report.

Mutations in SURF1, an assembly gene for cytochrome c oxidase (COX), the fourth complex of the oxidative phosphorylation system, are most frequently encountered in patients with COX deficiency. We describe a patient with Leigh syndrome harbouring a mutation in SURF1 who was reported decades ago with a tissue-specific cytochrome c oxidase deficiency.

Proteomics and neuromuscular diseases: theoretical concept and first results.

Although many patients suspected of suffering disturbances of the mitochondrial energy metabolism have been investigated, only a fraction of these patients have been diagnosed at the molecular level. Introduction of new techniques like proteomics will be necessary to understand the various clinical and biochemical aberrations in the field of mitochondrial disorders. Two-dimensional electrophoresis is the first, important step in the proteomics strategy. Separation of soluble proteins is performed on the basis of isoelectric point (net charge) in one direction and on molecular mass in the other. The technique provides an overview of the majority of proteins expressed in a sample (e.g. muscle biopsy, muscle cell or mitochondrial fraction). Once an abnormal spot is observed in the gel the responsible protein can be identified by analysing a limited part of its amino acid sequence by mass spectrometry. We optimized two-dimensional (2D) gel electrophoresis to obtain high resolution 2D-maps and tested the reproducibility of the technique. Potentially, this new technique is capable of identifying novel mitochondrial diseases and defining their molecular basis.

Shy1p occurs in a high molecular weight complex and is required for efficient assembly of cytochrome c oxidase in yeast.

Surf1p is a protein involved in the assembly of mitochondrial respiratory chain complexes. However its exact role in this process remains to be elucidated. We studied SHY1, the yeast homologue of SURF1, with an aim to obtain a better understanding of the molecular pathogenesis of cytochrome c oxidase (COX) deficiency in SURF1 mutant cells from Leigh syndrome patients. Assembly of COX was analysed in a shy1 null mutant strain by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Steady-state levels of the enzyme were found to be strongly reduced, the total amount of assembled complex being approximately 30% of control. The presence of a significant amount of holo-COX in the SHY1-disruptant strain suggests that Shy1p may either facilitate assembly of the enzyme, or increase its stability. However, our observations, based on 2D-PAGE analysis of mitochondria labelled in vitro, now provide the first direct evidence that COX assembly is impaired in a Deltashy1 strain. COX enzyme assembled in the absence of Shy1p appears to be structurally and enzymically normal. The in vitro labelling studies additionally indicate that mitochondrial translation is significantly increased in the shy1 null mutant strain, possibly reflecting a compensatory mechanism for reduced respiratory capacity. Protein interactions of both Shy1p and Surf1p are implied by their appearance in a high molecular weight complex of about 250 kDa, as shown by 2D-PAGE.