Temperature-induced changes in copper centers and protein conformation of two fungal laccases from Coriolus hirsutus and Coriolus zonatus

The paper reports on two fungal laccases from Coriolus hirsutus and Coriolus zonatus and their type-2 copper-depleted derivatives. Temperature-induced changes of the copper centers were characterized by optical and electron paramagnetic resonance (EPR) spectroscopy, and the overall protein stability by differential scanning microcalorimetry. The intact enzymes showed highly cooperative thermal unfolding transitions at about 90 degreesC. Type-2 copper depletion led to uncoupling of the domains characterized by a different melting pattern which resolved three subtransitions. Melting curves monitored optically at 290, 340 and 610 nm showed additional transitions below thermal unfolding temperature. EPR spectra of the intact laccases showed the disintegration of the trinuclear copper cluster accompanied by loss of one of the copper ions and disappearance of the strong antiferromagnetic coupling in the type-3 site at 70 degreesC and above 70 degreesC. The copper centers of type-2 copper-depleted laccase showed reduced thermotolerance. (C) 2001 Elsevier Science B,V. All rights reserved.