Metal-responsive elements in Pleurotus ostreatus laccase gene promoters

Abstract

Fungal laccase gene transcription is strongly induced by copper ions; notably, some laccase promoters contain multiple putative metal-responsive elements (MREs). Previously, it has been demonstrated that the Pleurotus ostreatus laccase genes poxc and poxa1b are transcriptionally induced by copper, and several putative MREs were found in the promoter regions of these genes, which extend for about 400 nt upstream of the start codon (ATG). Identification of MRE sequences, which are protected by protein binding in the poxc and poxa1b promoter regions, has been achieved by footprinting analyses. Electromobility shift assays led to the evaluation of the ability of the identified MREs to bind protein(s), and the role of specific nucleotides of these elements in complex formation has also been analysed. The formation of complexes between analysed MREs and fungal proteins requires the absence of metal ions. Proteins extracted from fungus grown in copper-depleted medium are able to form complexes with MREs, whilst proteins extracted from fungus grown in copper-containing medium are able to form complexes only in the presence of a metal chelator. Moreover, copper-depleted proteins are unable to form complexes when copper or zinc ions are added. UV-cross-linking analyses led to the determination of the molecular masses of the MRE-binding proteins. In the poxa1b promoter, a GC-rich region, homologous to the core binding site for transcription factor Sp1, decreases the binding affinity of the adjacent MRE, affecting its interactions with fungal protein factors.

Laccases: a never-ending story

“…Thus, the involvement of a negative-acting regulatory factor in metal response has been proposed. Moreover, in poxa1b promoter, a GC-rich region homologous to the core binding site for transcription factor Sp1 has been found to decrease the binding affinity of the adjacent MRE, affecting its interactions with fungal protein factors [161].…”

Influence of Trace Elements on Ligninolytic Enzyme Activity of Pleurotus ostreatus and P. pulmonarius

“…Laccase induction could be the result of limited selectivity of the metal-responsive promoter in the laccase gene in P. ostreatus, in which transcription can be controlled by several metal ions, including Zn (Faraco et al 2003). These authors explained the inhibitory effect of Zn by reduction of its affinity to bind to metal-regulatory protein that functions as a transcription factor.…”

“…However, in greater concentrations they could be toxic (Baldrian and Gabriel 2002;Baldrian 2003). Additionally, trace elements such as Fe, Zn, and Se could act through metal-responsive promoter interaction, to have posttranscriptional regulation and to cause oxidative stress (Thiele 1992;Faraco et al 2003;Catal et al 2008). Microelements in the plant raw materials are either present in a non-toxic amount, or they are not available, or they are in extractable forms.…”

Optimization of laccase production in the white-rot fungusPleurotus ostreatus(ACCC 52857) induced through yeast extract and copper

“…[12,15,20,21] The regulation of laccase expression by metals is widespread in fungi. [10] Copper induces the laccase activity in almost all fungi, and in Trametes versicolor, [7] P. sajor-caju, [21] Ceriporiopsis subvermispora, [22] Pleurotus ostreatus [23] and Trametes pubescens, [24] the copper-mediated regulation of laccase occurs at the transcription level. Other metals, such as Fe, Mn and Zn, also increase the laccase activity.…”