Structural and functional consequences of succinate dehydrogenase subunit B mutations
Mitochondrial dysfunction, due to mutations of the gene encoding succinate dehydrogenase (SDH), has been implicated in the development of adrenal phaeochromocytomas, sympathetic and parasympathetic paragangliomas, renal cell carcinomas, gastrointestinal stromal tumours and more recently pituitary tumours. Underlying mechanisms behind germline SDH subunit B (SDHB) mutations and their associated risk of disease are not clear. To investigate genotype–phenotype correlation of SDH subunit B (SDHB) variants, a homology model for humanSDHwas developed from a crystallographic structure.SDHBmutations were mapped, and biochemical effects of these mutations were predictedin silico. Results of structural modelling indicated that many mutations withinSDHBare predicted to cause either failure of functionalSDHBexpression (p.Arg27*, p.Arg90*, c.88delC and c.311delAinsGG), or disruption of the electron path (p.Cys101Tyr, p.Pro197Arg and p.Arg242His). GFP-tagged WTSDHBand mutantSDHBconstructs were transfected (HEK293) to determine biological outcomes of these mutantsin vitro. According toin silicopredictions, specificSDHBmutations resulted in impaired mitochondrial localisation and/or SDH enzymatic activity. These results indicated strong genotype–functional correlation forSDHBvariants. This study reveals new insights into the effects ofSDHBmutations and the power of structural modelling in predicting biological consequences. We predict that our functional assessment ofSDHBmutations will serve to better define specific consequences for SDH activity as well as to provide a much needed assay to distinguish pathogenic mutations from benign variants.