The arg-gly-asp (RGD) peptide sequence, which is found on animal-derived extracellular matrix (ECM) molecules such as fibronectin, mediates the adhesion of cells to the matrix. However, these ECM proteins are derived primarily as byproducts of animal agriculture, which is not sustainable, and risks microbial contamination. By datamining protein databases of fungi and plant species for the RGD sequence, it was surprisingly found that in 98% of these species, at least 1% of the reported proteins harbour RGD! While pathogenic fungi such as C. albicans often had a high RGD content, so did many edible mushroom species as enoki (F. velutipes), shiitake (L. edodes) and king oyster mushroom (P. eryngii).
Upon obtaining the protein extracts from these mushrooms, we made an interesting observation. Precipitation of a white particulate material occurred for all three extracts at room temperature, but at different rates. Precipitation could be slowed down by keeping the extracts in the refrigerator and accelerated by boiling them. Importantly, we could resuspend the collected particulates in water to form a fine, homogenous suspension (bottom pic, right) that could function as a cell-adhesive matrix for cell culture.
In a nutshell, we developed a method to obtain particulate extracts from these edible fungi and showed how they could support adhesion of muscle cells, at a level comparable to animal ECM proteins. A main motivation for the cell-cultivated food endeavour is sustainability, and for this, it requires the development of new sustainable materials and technologies. Although the fungus-derived cell adhesive factors introduced in our work may only be a cog in the wheel, we hope that they form a useful one, in the drive towards a sustainable future.