Partial purification of proteinase K inhibitors from liquid-cultured mycelia of the white rot basidiomycete Trametes versicolor

Characterization of a Novel Protease Inhibitor from the Edible Mushroom Agaricus bisporus

Background:

Protease inhibitors inhibit the activity of protease enzymes, hence are essentially involved in the regulation of the metabolic processes involving protease enzymes and protection the host organism against external damage due to proteases. These inhibitors are abundantly present in all living organisms but have not been much reported in mushrooms. Mushrooms are one of the major food components of humans with delicious taste and high nutritional value. Mushrooms also have therapeutic and economic significance. The edible mushrooms with medicinal properties are much in commercial demand. To date, the presence of protease inhibitors has not been reported much in edible mushrooms. The present study reports the characterization of a protease inhibitor isolated from the common white button mushroom Agaricus bisporus.

Objective:

The objective of the present study is to characterize the novel protease inhibitor from Agaricus bisporus to determine its nature and activity at varying environmental conditions.

Method:

The protease inhibitor was characterized through SDS PAGE, gel filtration chromatography, and de novo sequencing to determine its molecular mass, and sequence respectively. The optimum pH and temperature, and the pH and thermal stability were studied to determine the optimum working range of the protease inhibitor. The protease inhibitory activity (%) was determined in presence of metal ions, surfactants, oxidizing agents, and reducing agents. The kinetic parameters and the type of inhibition exhibited by the protease inhibitor were determined using casein and trypsin protease enzyme.

Results:

The protease inhibitor was found to be a low molecular mass compound of 25 kDa. The de novo sequencing matched the inhibitor against a 227 amino acid containing peptide molecular mass of 24.6 kDa molecular mass. The protease inhibitory activity (%) was found highest at pH 7.0 and temperature 50 0C, and was stable from pH 4.0-9.0 and temperature 30-80 0C. In presence of metal ions, the residual protease inhibitory activity (%) enhanced in presence of Na+, Mg2+, and Fe3+. The residual activity increased in presence of the surfactant SDS slightly in comparison to control, while decreased in the case of Triton-X and Tween 20. The presence of oxidizing agents, hydrogen peroxide, and dimethyl sulfoxide decreased the residual inhibitory activity. The protease inhibitor was unaffected by the reducing agents: dithiothreitol and β-mercaptoethanol up to 2mM concentration but decreased at higher concentrations. The inhibitor exhibited uncompetitive inhibition against trypsin with an inhibitory constant of 166 nM, indicating a strong affinity towards the protease, with a half-life of 93.90 minutes at 37 0C.

Conclusion:

Protease inhibitors isolated from mushrooms are generally small in size, more stable, and tolerant towards varying external conditions. The protease inhibitor isolated from Agaricus bisporus also exhibited similar characteristics.

Insights into the Role of Tick Salivary Protease Inhibitors during Ectoparasite-Host Crosstalk

Protease inhibitors (PIs) are ubiquitous regulatory proteins present in all kingdoms. They play crucial tasks in controlling biological processes directed by proteases which, if not tightly regulated, can damage the host organism. PIs can be classified according to their targeted proteases or their mechanism of action. The functions of many PIs have now been characterized and are showing clinical relevance for the treatment of human diseases such as arthritis, hepatitis, cancer, AIDS, and cardiovascular diseases, amongst others. Other PIs have potential use in agriculture as insecticides, anti-fungal, and antibacterial agents. PIs from tick salivary glands are special due to their pharmacological properties and their high specificity, selectivity, and affinity to their target proteases at the tick-host interface. In this review, we discuss the structure and function of PIs in general and those PI superfamilies abundant in tick salivary glands to illustrate their possible practical applications. In doing so, we describe tick salivary PIs that are showing promise as drug candidates, highlighting the most promising ones tested in vivo and which are now progressing to preclinical and clinical trials.

Fungal inhibitors of proteolytic enzymes: classification, properties, possible biological roles, and perspectives for practical use

Peptidase inhibitors are ubiquitous regulatory proteins controlling catalytic activity of proteolytic enzymes. Interest in these proteins increased substantially after it became clear that they can be used for therapy of various important diseases including cancer, malaria, and autoimmune and neurodegenerative diseases. In this review we summarize available data on peptidase inhibitors from fungi, emphasizing their properties, biological role, and possible practical applications of these proteins in the future. A number of fungal peptidase inhibitors with unique structure and specificity of action have no sequence homology with other classes of peptidase inhibitors, thus representing new and specific candidates for therapeutic use. The main classifications of inhibitors in current use are considered. Available data on structure, mechanisms and conditions of action, and diversity of functions of peptidase inhibitors of fungi are analyzed. It is mentioned that on one side the unique properties of some inhibitors can be used for selective inhibition of peptidases responsible for initiation and development of pathogenic processes. On the other side, general inhibitory activity of other inhibitors towards peptidases of various catalytic classes might be able to provide efficient defense of transgenic plants against insect pests by overcoming compensatory synthesis of new peptidases by these pests in response to introduction of a fungal inhibitor. Together, the data analyzed in this review reveal that fungal inhibitors extend the spectrum of known peptidase inhibitors potentially suitable for use in medicine and agriculture.

Structural basis of trypsin inhibition and entomotoxicity of cospin, serine protease inhibitor involved in defense of Coprinopsis cinerea fruiting bodies

Cospin (PIC1) from Coprinopsis cinerea is a serine protease inhibitor with biochemical properties similar to those of the previously characterized fungal serine protease inhibitors, cnispin from Clitocybe nebularis and LeSPI from Lentinus edodes, classified in the family I66 of the MEROPS protease inhibitor classification. In particular, it exhibits a highly specific inhibitory profile as a very strong inhibitor of trypsin with K(i) in the picomolar range. Determination of the crystal structure revealed that the protein has a β-trefoil fold. Site-directed mutagenesis and mass spectrometry results have confirmed Arg-27 as the reactive binding site for trypsin inhibition. The loop containing Arg-27 is positioned between the β2 and β3 strands, distinguishing cospin from other β-trefoil-fold serine protease inhibitors in which β4-β5 or β5-β6 loops are involved in protease inhibition. Biotoxicity assays of cospin on various model organisms revealed a strong and specific entomotoxic activity against Drosophila melanogaster. The inhibitory inactive R27N mutant was not entomotoxic, associating toxicity with inhibitory activity. Along with the abundance of cospin in fruiting bodies of C. cinerea and the lack of trypsin-like proteases in the C. cinerea genome, these results suggest that cospin and its homologs are effectors of a fungal defense mechanism against fungivorous insects that function by specific inhibition of serine proteases in the insect gut.

Trypsin-specific inhibitors from the basidiomycete Clitocybe nebularis with regulatory and defensive functions

We have isolated serine protease inhibitors from the basidiomycete Clitocybe nebularis, CnSPIs, using trypsin affinity chromatography. Full-length gene and cDNA sequences were determined for one of them, named cnispin, and the recombinant protein was expressed in Escherichia coli at high yield. The primary structure and biochemical properties of cnispin are very similar to those of the Lentinus edodes serine protease inhibitor, until now the only member of the I66 family of protease inhibitors in the MEROPS classification. Cnispin is highly specific towards trypsin, with K i in the nanomolar range. It also exhibited weaker inhibition of chymotrypsin and very weak inhibition of subtilisin and kallikrein; other proteases were not inhibited. Inhibitory activity against endogenous proteases from C. nebularis revealed a possible regulatory role for CnSPIs in the endogenous proteolytic system. Another possible biological function in defence against predatory insects was indicated by the deleterious effect of CnSPIs on the development of larvae of Drosophila melanogaster. These findings, together with the biochemical and genetic characterization of cnispin, suggest a dual physiological role for this serine protease inhibitor of the I66 MEROPS family.