BACKGROUND: Tyrosinase (TYR) catalyzes the rate-limiting, first step in melanin 
production and its gene (TYR) is mutated in many cases of oculocutaneous 
albinism (OCA1), an autosomal recessive cause of childhood blindness. Patients 
with reduced TYR activity are classified as OCA1B; some OCA1B mutations are 
temperature-sensitive. Therapeutic research for OCA1 has been hampered, in part, 
by the absence of purified, active, recombinant wild-type and mutant human 
enzymes.
METHODOLOGY/PRINCIPAL FINDINGS: The intra-melanosomal domain of human tyrosinase 
(residues 19-469) and two OCA1B related temperature-sensitive mutants, R422Q and 
R422W were expressed in insect cells and produced in T. ni larvae. The short 
trans-membrane fragment was deleted to avoid potential protein insolubility, 
while preserving all other functional features of the enzymes. Purified 
tyrosinase was obtained with a yield of >1 mg per 10 g of larval biomass. The 
protein was a monomeric glycoenzyme with maximum enzyme activity at 37°C and 
neutral pH. The two purified mutants when compared to the wild-type protein were 
less active and temperature sensitive. These differences are associated with 
conformational perturbations in secondary structure.
CONCLUSIONS/SIGNIFICANCE: The intramelanosomal domains of recombinant wild-type 
and mutant human tyrosinases are soluble monomeric glycoproteins with activities 
which mirror their in vivo function. This advance allows for the structure - 
function analyses of different mutant TYR proteins and correlation with their 
corresponding human phenotypes; it also provides an important tool to discover 
drugs that may improve tyrosinase activity and treat OCA1.