Characteristics of intracellular peptidase and proteinase activities from the mycelium of a cord-forming wood decay fungus, Serpula lacrymans

Abstract

Serpula lacrymans is a basidiomycete cord-forming wood decay fungus which reallocates nitrogen within an extensive perennial mycelial system in response to spatial discontinuities in external nutrient supply. Intracellular stored protein is mobilised by conversion to amino acids at nutrient-poor sites within a mycelium or when a whole mycelium is starved. Intracellular peptidase and proteinase activities of the mycelium were investigated with the aim of identifying proteases specifically activated in response to a nitrogen demand. Mycelium for enzyme extraction grown as surface mats in static liquid culture was homogenised, and the extract used in assays for proteinase and peptidase with various synthetic peptide substrates conjugated to 4-nitroaniline. Activities against different substrates were characterised with respect to pH, inhibitor sensitivity, requirements for divalent metal ions, isoelectric point, and by changes in activities in starved mycelium. Four different activities were found, comprising two peptidases one of which had metalloprotease characteristics, a serine-type proteinase, and a proteinase active at pH 2.5 which was not affected by any of the inhibitors tried. Both the latter were most active in starved mycelium. Isoelectric focusing showed peaks with activities corresponding to the serine-type proteinase and one of the manganese-activated peptidases. Possible roles for these enzymes in nitrogen reallocation during mycelial foraging are discussed.

Activation of caspase-like activity and poly (ADP-ribose) polymerase degradation during sporulation in Aspergillus nidulans

“…There is good evidence that breakdown of material for reuse in other mycelial parts occurs within intact cell membranes (Lilly et al, 1991;Watkinson et al, 2001) and thus resembles apoptosis in animal cells (Olsson, 2001). Searches for homologues of Fig.…”

The role of wood decay fungi in the carbon and nitrogen dynamics of the forest floor

“…Starvation-induced proteinases have been investigated with a view to developing a suitable reporter for identifying sites in the mycelium where autolysis and regression are induced. A serine proteinase activity was identified in Serpula lacrymans with characteristics consistent with a role in mobilizing intracellular protein stores from cytoplasm, as well as a lysosomal-type activity optimal at low pH (Watkinson et al, 2001;Wadekar et al, 1995). Genes for serine proteinases of several cord-forming wood decay fungi have been cloned (Eastwood & Tlalka, unpublished; Eastwood & Higgins, unpublished) and show homology to other fungal serine proteinases with putative roles in internal protein mobilization (Kingsnorth et al, 2001).…”

Serpula lacrymans, Wood and Buildings

“…lacrymans commonly associated with the built environment. We hypothesize that responses to nitrogen status, including cord development, and the induction of an intracellular lysosomal-type proteinase activity (Watkinson et al, 2001) not found in other fungi investigated, might be mediated through changes in intracellular amino acid. Scavenging mycelium colonizes a new wood food source, inducing variegatic acid (VA) production, and expression of oxidoreductase enzymes which drive hydroxyl radical attack on the lignocellulose composite.…”