Characterization of SURF-1 expression and Surf-1p function in normal and disease conditions

Valeria Tiranti, Claudia Galimberti, Leo Nijtmans, Silvia Bovolenta, Maria Paola Perini, Massimo Zeviani

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Abstract

Loss-of-function mutations of the SURF-1 gene have been associated with Leigh syndrome with cytochrome c oxidase (COX) deficiency. Mature Surf-1 protein (Surf-1p) is a 30 kDa hydrophobic polypeptide whose function is still unknown. Using antibodies against a recombinant, hemagglutinin-tagged Surf-1p, we have demonstrated that this protein is imported into mitochondria as a larger precursor, which is then processed into the mature product by cleaving off an N-terminal leader polypeptide of ~ 40 amino acids. By using western blot analysis with specific antibodies, we showed that Surf-1p is localized in and tightly bound to the mitochondrial inner membrane. The same analysis revealed that no protein is present in cell lines harboring loss-of-function mutations of SURF-1, regardless of their type and position. Northern blot analysis showed the virtual absence of specific SURF-1 transcripts in different mutant cell lines. This result suggests that several mutations of SURF-1 are associated with severe mRNA instability. To understand better whether and which domains of the protein are essential for function, we generated several constructs with truncated or partially deleted SURF-1 cDNAs. None of these constructs, expressed into Surf-1p null mutant cells, were able to rescue the COX phenotype, suggesting that different regions of the protein are all essential for function. Finally, experiments based on blue native two-dimensional gel electrophoresis indicated that assembly of COX in Surf-1p null mutants is blocked at an early step, most likely before the incorporation of subunit II in the nascent intermediates composed of subunit I alone or subunit I plus subunit IV. However, detection of residual amounts of fully assembled complex suggests a certain degree of redundancy of this system.

Original languageEnglish
Pages (from-to)2533-2540
Number of pages8
JournalHuman Molecular Genetics
Volume8
Issue number13
Publication statusPublished - 1999

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ASJC Scopus subject areas

  • Genetics

Cite this

Tiranti, V., Galimberti, C., Nijtmans, L., Bovolenta, S., Perini, M. P., & Zeviani, M. (1999). Characterization of SURF-1 expression and Surf-1p function in normal and disease conditions. Human Molecular Genetics, 8(13), 2533-2540.