In terrestrial environments, Nostoc commune colonies are subjected to desiccation and UV-irradiation. Protective compounds that are involved in reactive oxygen-scavenging mechanisms must have an important role in increasing cell tolerance to the oxidative stresses associated with desiccation and UV irradiation. Mycosporine-like amino acids (MAAs) function mainly to protect the cells against UV-induced oxidative stress. MAAs are water-soluble pigments that absorb specific UV-B radiation in the range of 280 to 320 nm. They are also thought to be the strongest UVA-absorbing compounds in nature. With their photoprotective and antioxidative properties, MAAs are natural bioactive compounds attractive to cosmeceutical and pharmaceutical applications. In this study, the water extract of N. commune colony with absorption maxima at 312 and 340 nm was studied and three structurally novel MAAs were characterized. The extract contained hybrid MAAs (1050 Da and 880 Da) with two distinct chromophores of 3-aminocyclohexen-1-one and 1,3-diaminocyclohexen linked to 2-O-(β-xylopyranosyl)-β-galactopyranoside. A novel 273-Da MAA with an absorption maximum at 310 nm was also identified which consisted of a 3-aminocyclohexen-1-one linked to a γ-aminobutyric acid chain. The 1050-Da, 880-Da and 273-Da MAAs accounted for approximately 43%, 16% and 8% of the total MAAs, respectively. These MAAs had potent radical scavenging activities in vitro; the 1050-Da, 880-Da and 273-Da MAAs contributed approximately 27%, 12% and 5% of the total radical scavenging activities in a water extract of N. commune. The results confirmed that the MAAs have multiple roles as a UV protectant and an antioxidant relevant to anhydrobiosis in N. commune. With these MAAs, N.commune is thought to be able to adapt to terrestrial environments with high levels of solar radiation.
