Multifunctions of MelB, a fungal tyrosinase from Aspergillus oryzae.
The pro form of melB tyrosinase from the melB gene of Aspergillus oryzae was over-produced from E. coli and formed a homodimer that exhibited the spectral features of met-tyrosinase. In the presence of NH(2)OH (reductant), the proenzyme bound dioxygen to give a stable (μ-η(2):η(2) -peroxo)dicopper(II) species (oxy form), thus indicating that the pro form tyrosinase can function as an oxygen carrier or storage protein like hemocyanin. The pro form tyrosinase itself showed no catalytic activity toward external substrates, but proteolytic digestion with trypsin activated it to induce tyrosinase activity. Mass spectroscopy analyses, mutagenesis experiments, and colorimetry assays have demonstrated that the tryptic digestion induced cleavage of the C-terminal domain (Glu458-Ala616), although the dimeric structure of the enzyme was retained. The structural changes induced by proteolytic digestion might open the entrance to the enzyme active site for substrate incorporation.
Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan. fujieda@mls.eng.osaka-u.ac.jp
Nobutaka
N
Fujieda
Michiaki
M
Murata
Shintaro
S
Yabuta
Takuya
T
Ikeda
Chizu
C
Shimokawa
Yukihiro
Y
Nakamura
Yoji
Y
Hata
Shinobu
S
Itoh
D000595:Amino Acid Sequence; D000818:Animals; D001236:Aspergillus oryzae / Q000201:enzymology*; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008974:Mollusca / Q000737:chemistry / Q000201:enzymology / Q000235:genetics; D014442:Monophenol Monooxygenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D014442:Monophenol Monooxygenase