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Synthesis and biodegradation of marine cyclopeptides derived from laxaphycin B

Abstract : Due to climate change, the lagoon of Moorea in French Polynesia is impacted by cyanobacteria blooms asphyxiating corals, causing reef degradation and decreasing food resources. Lyngbya majuscula and Anabaena torulosa are two filamentous benthic cyanobacteria that proliferate on sand and corals. They produce many secondary metabolites that can be toxic. Anabaena torulosa produces cyclic lipopeptides such as laxaphycins A and B, composed of 11 and 12 amino acids, respectively. This cyanobacterium has been able to develop chemical strategies of protection against grazers, which can be repelled by the toxic molecules produced such as laxaphycin B. In turn, herbivores must circumvent these defenses and in some cases even take advantage of them to protect themselves from their own predators. This is the case of Stylocheilus striatus, a sea hare that feeds on Lyngbya majuscula and Anabaena torulosa, and appears to be less susceptible to predation on Anabaena torulosa. Stylocheilus striatus consumes the latter without being affected by laxaphycin B toxicity. To overcome this toxicity, the sea hare has developed an adaptive mechanism that allows the biotransformation of laxaphycin B into non-toxic acyclic laxaphycin B. While non-toxic laxaphycin A is bioaccumulated in its digestive gland, laxaphycin B undergoes two successive cleavages at the C-terminal position of two hydroxyleucines. In order to study the enzymatic mechanism involved in this biotransformation, we have synthesized various analogues of laxaphycin B. First, we optimized their chemical synthesis, allowing us to confirm the structure of trichormamide C, a natural peptide analogous to laxaphycin B. In a second step, the synthesized analogues could be submitted to the studied enzyme and showed the reproducibility of the cleavage on different sequences. First characteristics of the enzyme could be identified, such as its cleavage specificities. Finally, our efforts focused on the design of a minimal peptide sequence for the recognition of the enzyme, in order to consider different strategies to isolate it.
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Submitted on : Thursday, November 25, 2021 - 1:33:41 PM
Last modification on : Friday, November 26, 2021 - 3:45:47 AM

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  • HAL Id : tel-03448836, version 1

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Laurine Darcel. Synthesis and biodegradation of marine cyclopeptides derived from laxaphycin B. Inorganic chemistry. Université de Perpignan, 2021. English. ⟨NNT : 2021PERP0022⟩. ⟨tel-03448836⟩

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