Stability of non-proteinogenic amino acids to UV and gamma irradiation

Abstract

Almost all living organisms on Earth utilize the same 20 amino acids to build their millions of different proteins, even though there are hundreds of amino acids naturally occurring on Earth. Although it is likely that both the prebiotic and the current environment of Earth shaped the selection of these 20 proteinogenic amino acids, environmental conditions on extraterrestrial planets and moons are known to be quite different than those on Earth. In particular, the surfaces of planets and moons such as Mars, Europa and Enceladus have a much greater flux of UV and gamma radiation impacting their surface than that of Earth. Thus, if life were to have evolved extraterrestrially, a different lexicon of amino acids may have been selected due to different environmental pressures, such as higher radiation exposure. One fundamental property an amino acid must have in order to be of use to the evolution of life is relative stability. Therefore, we studied the stability of three different proteinogenic amino acids (tyrosine, phenylalanine and tryptophan) as compared with 20 non-proteinogenic amino acids that were structurally similar to the aromatic proteinogenic amino acids, following ultraviolet (UV) light (254, 302, or 365 nm) and gamma-ray irradiation. The degree of degradation of the amino acids was quantified using an ultra-high performance liquid chromatography-mass spectrometer (UPLC-MS). The result showed that many non-proteinogenic amino acids had either equal or increased stability to certain radiation wavelengths as compared with their proteinogenic counterparts, with fluorinated phenylalanine and tryptophan derivatives, in particular, exhibiting enhanced stability as compared with proteinogenic phenylalanine and tryptophan amino acids following gamma and select UV irradiation.

Marine Science Can Contribute to the Search for Extra-Terrestrial Life

“…One other important term for all three clusters is “biosignature” ( Figure S2 ). Missions seeking bio-signatures in situ on Mars and icy moons of our Solar System are a challenging task because organisms and their metabolic products may be destroyed by the harsh conditions experienced on irradiated planetary and icy-moon surfaces [ 114 , 115 , 116 , 117 , 118 ]. Bio-signature search in distant exo-planets is a rather different task and focuses on the spectral analysis of atmospheres.…”

Degradation of Amino Acids on Mars by UV Irradiation in the Presence of Chloride and Oxychlorine Salts

“…However, organic compounds or evidence of life could still be present where it has been sheltered from exposure to radiation (Stalport et al, 2019;Tan and Sephton, 2019;Fornaro et al 2018;Pavlov et al, 2012). (Laurent et al, 2019;Rowe et al, 2019;Bertrand et al, 2015;Stalport et al, 2019;ten Kate et al, 2005;). For example, it has been shown that a thin film of glycine has a half-life of 22±5 h when irradiated under UV between 120-180 nm at room temperature, but modelling and experiments have shown that its half-life can be extended on the order of 10 7 years when protected by inert martian regolith (ten Kate et al, 2005).…”

“…The destructive effect of UV radiation seems to involve more than just the photon energy of the different wavelengths. Using tryptophan and tryptophan analogues, it has been shown that UVB (280-315 nm) has greater destructive power than the higher energy UVC (100-280 nm) (Rowe et al, 2019).…”