Protein expression and identification of Tyrp1 Mutant Variants Associated with OCA3 form of albinism.

Oculocutaneous albinism type 3 (OCA3) is an autosomal recessive disorder caused by mutations in the TYRP1 gene. Tyrosinase-related protein 1 (Tyrp1) is involved in eumelanin synthesis, catalyzing the oxidation of 5,6-dihydroxyindole-2-carboxylic acid oxidase (DHICA) to 5,6-indolequinone-2-carboxylic acid (IQCA). In our work, we are trying to understand the effect of genetic mutations at the level of protein atomic structure and establish a link between the effect of mutations and disease phenotype. Here, for the first time, four OCA3-causing mutations of Tyrp1, C30R, H215Y, D308N, and R326H, were investigated computationally and experimentally to understand Tyrp1 protein stability and catalytic activity. Using the Tyrp1 crystal structure (PDB:5M8L), global mutagenesis was conducted to evaluate mutant protein stability. Consistent with our predictions the foldability parameter, C30R and H215Y should exhibit greater instability, and two other mutants, D308N and R326H, are expected to keep a native conformation. Mass-spectroscopy analysis has confirmed the identity of mutant recombinant variants. SDS-PAGE and Western blot analysis of the purified recombinant proteins confirmed that the foldability parameter correctly predicted the effect of mutations critical for protein stability.