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. 2020 Apr 20;10(4):45.
doi: 10.3390/life10040045.

pH-Dependent Adsorption of Peptides on Montmorillonite for Resisting UV Irradiation

Rongcan Lin  1 , Yueqiao Wang  1 , Xin Li  1 , Yan Liu  1 , Yufen Zhao  1   2   3
Affiliations

pH-Dependent Adsorption of Peptides on Montmorillonite for Resisting UV Irradiation

Rongcan Lin et al. Life (Basel). .

Abstract

Ultraviolet (UV) irradiation is considered an energy source for the prebiotic chemical synthesis of life's building blocks. However, it also results in photodegradation of biology-related organic compounds on early Earth. Thus, it is important to find a process to protect these compounds from decomposition by UV irradiation. Herein, pH effects on both the adsorption of peptides on montmorillonite (MMT) and the abilities of peptides to resist UV irradiation due to this adsorption were systematically studied. We found that montmorillonite (MMT) can adsorb peptides effectively under acidic conditions, while MMT-adsorbed peptides can be released under basic conditions. Peptide adsorption is positively correlated with the length of the peptide chains. MMT's adsorption of peptides and MMT-adsorbed peptide desorption are both rapid-equilibrium, and it takes less than 30 min to reach the equilibrium in both cases. Furthermore, compared to free peptides, MMT-adsorbed peptides under acidic conditions are well protected from UV degradation even after prolonged irradiation. These results indicate amino acid/peptides are able to concentrate from aqueous solution by MMT adsorption under low-pH conditions (concentration step). The MMT-adsorbed peptides survive under UV irradiation among other unprotected species (storage step). Then, the MMT-adsorbed peptides can be released to the aqueous solution if the environment becomes more basic (releasing step), and these free peptides are ready for polymerization to polypeptides. Hence, a plausible prebiotic concentration-storage-release cycle of amino acids/peptides for further polypeptide synthesis is established.

Keywords: UV radiation protection; adsorption; montmorillonite; pH-dependent; peptides.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Figure 1
Figure 1
UV irradiation reaction device. Controls 1, 2 and 3 are three parallel control groups of the tested sample without MMT. Tests 1, 2 and 3 are three parallel experimental groups of the tested sample with MMT.
Figure 2
Figure 2
pH-dependent adsorption profile of Phe2 on MMT.
Figure 3
Figure 3
The time curves of adsorption at pH 3 (a) and desorption at pH 10 (b) of Phe2 on MMT.
Figure 4
Figure 4
XRD patterns of the initial MMT (black) and Pro2 adsorbed on MMT (red).
Figure 5
Figure 5
Rate of survival of Phe2 after exposure to UV radiation: (a) UV exposure time of 1 day. (b) UV exposure time of 5 days.
Figure 6
Figure 6
Survival rates of different peptides after exposure to UV radiation for 5 days at pH 3.
Figure 7
Figure 7
Unit cell of MMT [44] and a possible protection mechanism of MMT for peptides.
See this image and copyright information in PMC

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