Laccase (ЕС 1.10.3.2) belongs to the family of "blue" oxidoreductases containing in the active center four copper atoms organized in metal centers T1 and T2/T3. The T2/T3 center includes a T2 center with one copper atom and a T3 center with two copper atoms. Laccase catalyzes oxidation of a wide range of phenolic and non-phenolic substrates. The final electron acceptor is oxygen, which is reduced to water. Laccases are found in fungi, bacteria, plants and insects. Eukaryotic laccases consist of three domains, in bacteria, besides three-domain laccases there are two-domain (small) laccases. Two-domain laccases have high thermal stability, are active in the alkaline pH range and in the presence of different inhibitors of three-domain laccases. It is known that sodium azide is a strong inhibitor of three-domain laccase; structural methods show that it is located in the T2/T3-center of laccase. Two-domain laccases are poorly inhibited even by high concentrations of sodium azide, and their activity in the alkaline pH in the presence of sodium azide even increases. The site of binding of sodium azide with two-domain laccase was not determined. In this study, for the first time we have found a presumptive binding site of azide with small laccase Streptomyces sp. (lividans ) Ac-1709. Azide is found at a distance of about 5 Å from the substrate-binding pocket of the T1-center. In this paper we suggest an explanation of low sensitivity of two-domain laccase to sodium azide.
two-domain laccases, sodium azide, crystal structure, copper-containing centers
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