Human tyrosinase (Tyr) is a Type I membrane glycoprotein that is the rate-limiting enzyme for controlling the production of melanin pigment in melanosomes. Currently, ~300 Tyr mutations are known to be involved in the genetic disease oculocutaneous albinism type 1 (OCA1), which exists in two forms, OCA1A and OCA1B. OCA1A is caused by a full loss of Tyr enzymatic activity, resulting in the absence of pigment in the skin, hair, and eyes, while OCA1B has reduced Tyr activity and pigment. Here, we used molecular modeling to try to understand the role of genetic changes at the protein level in inherited disease. The significant part of Tyr intra-melanosomal domain and five OCA1 mutant variants were built by homology modeling, glycosylated in silico, and refined using molecular dynamics in water. The modeling confirmed experimental results that N347 and N371 glycosylation is vital for protein stability. The changes caused by the T373K mutation indicate a significant impact on protein structure, as expected for OCA1A. In addition, evaluation of free energy changes in OCA1B mutants showed a strong association with the changes observed in our unfolding/refolding experiments in vitro. In conclusion, our results could be useful for understanding the role of OCA1 mutant variants in melanin pigment production, in silico searching for inhibitors and activators of tyrosinase activity, and genotype-to- phenotype analysis in OCA1.
Keywords: albinism-causing mutations; homology modeling; human tyrosinase.