Analysis of protein biosynthesis errors in Candida albicans.

Recent works show that protein mistranslation is widespread in nature and that both single cell or multicellular organisms can take advantage of it, by regulating its levels, under specific physiological and environmental conditions. In C. albicans, it leads to increased morphological and physiological phenotypic diversity of high adaptive potential, but the scope of such protein mistranslation is poorly understood due to technical difficulties in detecting and quantifying amino acid misincorporation events in complex proteomic samples. The phenomenon of mistranslation has been extensively studied in the leucine CUG codon, which has been reassigned to either serine or alanine, or ambiguously assigned to serine and leucine in several fungal species of the so called CTG clade. Serine-to-leucine (Ser→Leu) ambiguous decoding has been observed in Ascoidea asiatica, Candida maltosa, C. albicans and more recently, in the halotolerant yeast Debaryomyces hansenii. In C. albicans, CUG translation is facilitated by a hybrid tRNA(CAG)Ser that contains identity elements for both seryl-tRNA synthetase (SerRS) and leucyl-tRNA synthetase (LeuRS). Under normal physiological conditions the tRNA(CAG)Ser is mainly aminoacylated with Ser by the SerRS (appx 97%). We have developed and optimized mass spectrometry and bioinformatics pipelines capable of identifying low-level amino acid misincorporation events at the proteome level and determine codons error frequencies. We have also analysed the proteomic profile of an engineered C. albicans strain that exhibits high level of leucine misincorporation at protein CUG sites.