Hemocyanins from Arthropods and Molluscs

Magnus, Karen A.

doi:10.1002/0470028637.met195

Handbook of Metalloproteins 2004

DOI: 10.1002/0470028637.met195

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Hemocyanins from Arthropods and Molluscs

Karen A. Magnus

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2006

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“…Tyrosinases have been shown to share a similar active site with catechol oxidase and hemocyanin, a protein involved in oxygen transport in arthropods and molluscs [11]. These proteins are type 3 copper proteins with a diamagnetic spin‐coupled copper pair in the active center.…”

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Production and characterization of a secreted, C‐terminally processed tyrosinase from the filamentous fungus Trichoderma reesei

et al. 2006

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Tyrosinase (monophenol, o-diphenol:oxygen oxidoreductase, EC 1.14.18.1) is a copper-containing metalloprotein that is ubiquitously distributed in nature. Tyrosinases are found in prokaryotic as well as in eukaryotic microorganisms, and in mammals, invertebrates and plants. Tyrosinase is a mono-oxygenase and a bifunctional enzyme that catalyzes the o-hydroxylation of monophenols and subsequent oxidation of o-diphenols to quinones [1,2]. The activities are also referred to as cresolase or monophenolase and catecholase or diphenolase activities, respectively. Tyrosinase thus accepts monophenols and diphenols as substrates, and the monophenolase activity is the initial rate-determining reaction [2,3]. A homology search of the genome database of the filamentous fungus Trichoderma reesei identified a new T. reesei tyrosinase gene tyr2, encoding a protein with a putative signal sequence. The gene was overexpressed in the native host under the strong cbh1 promoter, and the tyrosinase enzyme was secreted into the culture supernatant. This is the first report on a secreted fungal tyrosinase. Expression of TYR2 in T. reesei resulted in good yields, corresponding to approximately 0.3 and 1 gAEL )1 tyrosinase in shake flask cultures and laboratory-scale batch fermentation, respectively. T. reesei TYR2 was purified with a three-step purification procedure, consisting of desalting by gel filtration, cation exchange chromatography and size exclusion chromatography. The purified TYR2 protein had a significantly lower molecular mass (43.2 kDa) than that calculated from the putative amino acid sequence (61.151 kDa). According to N-terminal and C-terminal structural analyses by fragmentation, chromatography, MS and peptide sequencing, the mature protein is processed from the C-terminus by a cleavage of a peptide fragment of about 20 kDa. The T. reesei TYR2 polypeptide chain was found to be glycosylated at its only potential N-glycosylation site, with a glycan consisting of two N-acetylglucosamines and five mannoses. Also, low amounts of shorter glycan forms were detected at this site. T. reesei TYR2 showed the highest activity and stability within a neutral and alkaline pH range, having an optimum at pH 9. T. reesei tyrosinase retained its activity well at 30°C, whereas at higher temperatures the enzyme started to lose its activity relatively quickly. T. reesei TYR2 was active on both l-tyrosine and l-dopa, and it showed broad substrate specificity.Abbreviations TYR2, tyrosinase 2 from Trichoderma reesei; Q-TOF, quadrupole time-of-flight.

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Production and characterization of a secreted, C‐terminally processed tyrosinase from the filamentous fungus Trichoderma reesei

et al. 2006

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Hemocyanins from Arthropods and Molluscs

Cited by 1 publication

References 83 publications

Production and characterization of a secreted, C‐terminally processed tyrosinase from the filamentous fungus Trichoderma reesei

Production and characterization of a secreted, C‐terminally processed tyrosinase from the filamentous fungus Trichoderma reesei

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