A truncation library for the soluble production of squalene synthase from Candida albicans in Escherichia coli

The rising global burden of infectious fungal disease and the steady increase of resistance by fungal pathogens to available treatments necessitate a concerted effort to develop new antifungal medicines. Squalene synthase is a critical enzyme in the synthesis of ergosterol, a fungal-specific sterol, and has not yet been exploited as an antifungal drug target for pathogenic yeast. In this study, we heterologously produce squalene synthase (SQS) from the opportunistic pathogen Candida albicans in Escherichia coli to obtain high-quality pure protein for structural studies. A library of nine C- or N&C-terminally truncated SQS variants was successfully produced and purified with immobilised metal-affinity chromatography (IMAC). Two variants were upscaled and purified to near-homogeneity, but size-exclusion chromatography showed possible aggregation. Nevertheless, this study provides a starting point to further optimise buffer conditions to produce high-quality heterologous SQS from C. albicans for downstream crystallography experiments.