Analysis of laccase-like enzymes secreted by fungi isolated from a cave
in Northern Spain
Abstract
Laccases belong to a family of multicopper enzymes able to oxidize a
broad spectrum of organic compounds. Despite the well-known property of
laccases to carry out bleaching and degradation of industrial dyes and
polyphenolic compounds, their industrial use is often limited by the
high cost, low efficiency, or instability of these enzymes. To look for
new microorganisms which produce laccases that are potentially suitable
for industrial applications, we have isolated several fungal strains
from a cave in northern Spain. Their phenotypic analysis on agar plates
supplemented with ABTS (2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic
acid)) disclosed two laccase-positive strains. Further genotyping
revealed that they belonged to the Gliomastix murorum and Conidiobolus
thromboides species. The secretion of G. murorum and C. thromboides
laccase-like enzymes was then confirmed by zymography. Further
identification of these polypeptides by mass-spectroscopy revealed the
nature of the laccases and made it possible to predict their functional
domains and other features. In addition, plate assays revealed that the
laccases secreted by both G. murorum and C. thromboides were capable of
degrading industrial dyes (Congo Red, Indigo, and Eriochrome Black T).
Homology modeling and substrate docking predicted the putative structure
of the currently uncrystallized G. murorum enzyme as well as its amino
acid residues potentially involved in interactions with these dyes. In
summary, new biochemical and structural insights into decolorization
mediated by G. murorum laccase as well as identification of laccase-like
oxidase in C. thromboides point to a promising future for these enzymes
in biotechnology.