Ty. Tsai et Yhw. Lee, ROLES OF COPPER LIGANDS IN THE ACTIVATION AND SECRETION OF STREPTOMYCES TYROSINASE, The Journal of biological chemistry, 273(30), 1998, pp. 19243-19250
The expression of the melanin operon (melC) of Streptomyces antibiotic
us requires the chaperone-like protein MelC1 for the incorporation of
two copper ions (designated as Cu-A and Cu-B) and the secretion of the
apotyrosinase (MelC2) via a transient binary complex formation betwee
n these two proteins. To: investigate whether the copper ligand of tyr
osinase is involved in this MelC1 MelC2 binary complex function, six s
ingle substitution mutations were introduced into the Cu-A and CUB sit
es. These mutations led to differential effects on the stability, copp
er content, and export function of binary complexes but a complete abo
lishment of tyrosinase activity. The defects in the tyrosinase activit
y in mutants were not because of the impairment of the formation of Me
lC1 MelC2 complex but rather the failure of MelC2 to be discharged fro
m the copper-activated binary complex. Moreover, the impairments on th
e discharge of the mutant MelC2 from all the mutant binary complexes a
ppeared to result from the structural changes in their apoforms or cop
per-activated forms of the complexes, as evidenced by the fluorescence
emission and circular dichroism spectral analysis. Therefore, each of
six copper ligands in Streptomyces tyrosinase binuclear copper sites
plays a pivotal role in the final maturation and the discharge of tyro
sinase from the binary complex but has a less significant role in its
secretion.