Molecular interactions within the melanogenic complex: Formation of heterodimers of tyrosinase and TRP1 from B16 mouse melanoma

Melanin synthesis in mammals is catalyzed by three structurally related, me mbrane-bound proteins, tyrosinase, and the tyrosinase-related proteins 1 an d 2 (TRP1 and TRP2). Current evidence suggests that in vivo these proteins may form a multienzyme complex, However, neither the precise composition of the complex, nor the specific interactions between its components have bee n characterized. This study used purified preparations of tyrosinase and TR P1 to analyze their interactions in non ionic detergent solution. Purified tyrosinase and TRP1 behaved as homodimers as judged by gel filtration chrom atography and electrophoresis. Upon mixing of the purified proteins, the pr eferential formation of heterodimers was detected by: i) coelution in gel f iltration chromatography with a shift to a common partition coefficient for both proteins, and ii) the occurrence of fluorescent energy transfer betwe en fluorescein-labeled tyrosinase and rhodamine-labeled TRP1. However, the formation of heterodimers did not cause changes in the tyrosine hydroxylase activity of the enzymes, at least under standard assay conditions, Thus, t yrosinase and TRP1 interact strongly and specifically in detergent solution to form an heterodimer that might contribute to the formation of the melan ogenic complex. (C) 1998 Academic Press.