Orf239342 from the mushroom Agaricus bisporus is a mannose binding protein.

A recently discovered lectin-like protein from mushroom tyrosinase designated as orf239342 inhibits proliferation of the MCF-7 breast cancer cells. This characteristic is likely derived from its ability to recognize sugar entity on the cell surface. Thereby, the binding specificity of orf239342 to sugars was studied. Orf239342 was found to bind specifically to mannose upon analysis with the surface plasmon resonance technique. Finally, our in vitro study showed that mannose impeded orf239342 ability to inhibit proliferation of the MCF-7 breast cancer cells, providing further evidence for the mannose binding onto the protein. Our finding is a breakthrough to characterise orf239342 i.e. to define its functioning in the mushroom, association to the tyrosinase, or even possible application in breast cancer therapy. In addition, the finding allows the more appropriate designation of the protein as Agaricus bisporus mannose binding-protein (AbMb).

The light subunit of mushroom Agaricus bisporus tyrosinase: Its biological characteristics and implications.

The light subunit of mushroom Agaricus bisporus tyrosinase (LSMT) is a protein of unknown function that was discovered serendipitously during the elucidation of the crystal structure of the enzyme. The protein is non-immunogenic and can penetrate the intestinal epithelial cell barrier, and thus, similar to its structural homologue HA-33 from Clostridium botulinum, may be potentially absorbable by the intestine. LSMT also shares high structural homology with the ricin-B-like lectin from the mushroom Clitocybe nebularis (CNL), which has been shown to display biological activity against leukemic cancer cells and dendritic cells. Therefore, we evaluated the biological activity of LSMT. An in vitro assay suggested that LSMT presentation to most of the cancer cell lines studied has a negligible effect on their proliferation. However, inhibition of cell growth and a slight stimulation of cell proliferation were observed with breast cancer and macrophage cells, respectively. LSMT appeared to be relatively resistant against proteolysis by trypsin and papain, but not bromelain. Challenges with gastric and intestinal juice suggested that the protein is resistant to gastrointestinal tract conditions. This is the first report on the biological characteristics and implication of LSMT.