Antioxidant-Rich Peptide Fractions Derived from High-Altitude Chinese Caterpillar Medicinal Mushroom Ophiocordyceps sinensis (Ascomycetes) Inhibit Bacterial Pathogens

Ophiocordyceps sinensis (=Cordyceps sinensis), a medicinal mushroom native to the Orient, has been extensively used for the past few centuries in traditional Chinese medicine because of its immunomodulatory, antiinflammatory, and nutraceutical properties. In the present study, three antioxidant and antibacterial Ophiocordyceps peptide fractions (COPs) were separated from the Indian variety of O. sinensis on a Sephadex G-25 resin. Amide bonds in the COPs were confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Cationic and hydrophobic amino acids, which are reported to be the major constituent amino acids of antimicrobial peptides, were identified in the COPs by matrix-assisted laser desorption/ionization-mass spectrometry and high-performance liquid chromatography. Putative secondary structures were predicted by circular dichroism to be β-sheets and random coils. The COPs demonstrated substantial antioxidant potential by scavenging 2,2-diphenyl-l-picryl-hydrazyl-hydrate (median inhibitory concentration [IC50] values, 4.79-18.7 mg/mL) and 2,2'-azino-bis-3-ethylbenzothiazoline-6-sul-phonic acid (IC50 values, 4.51-14.05 mg/mL) free radicals and also by chelating heavy metal ions. Additionally, the peptide fractions were capable of significantly inhibiting bacterial pathogens viz. Escherichia coli and Salmonella typhi. The potential antibacterial mechanisms of action were established to be generation of reactive oxygen species and intracellular protein leakage within the bacterial cells.