The structure and synthetic capabilities of a catalytic peptide formed by substrate-directed mechanism - Implications to prebiotic catalysis

Gideon Fleminger*, Tal Yaron, Miriam Eisenstein, Akiva Bar-Nun

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Previously, we have shown that a small substrate may serve as a template in the formation of a specific catalytic peptide, a phenomenon which might have had a major role in prebiotic synthesis of peptide catalysts. This was demonstrated experimentally by the formation of a catalytic metallo-dipeptide, Cys2-Fe2+, around o-nitrophenyl β-D-galactopyranoside (ONPG), by dicyandiamide (DCDA)-assisted condensation under aqueous conditions. This dipeptide was capable of hydrolyzing ONPG at a specific activity lower only 1000 fold than that of β galactosidase. In the present paper we use molecular modeling techniques to elucidate the structure of this catalyst and its complex with the substrate and propose a putative mechanism for the catalyst formation and its mode of action as a "mini enzyme". This model suggests that interaction of Fe2+ ion with ONPG oxygens and with two cysteine SH groups promotes the specific formation of the Cys 2-Fe2+ catalyst. Similarly, the interaction of the catalyst with ONPG is mediated by its Fe2+ with the substrate oxygens, leading to its hydrolysis. In addition, immobilized forms of the catalyst were synthesized on two carriers - Eupergit C and amino glass beads. These preparations were capable of catalyzing the formation of ONPG from β-D-galactose and o-nitrophenol (ONP) under anhydrous conditions. The ability of the catalyst to synthesize the substrate that mediates its own formation creates an autocatalytic cycle where ONPG catalyzes the formation of a catalyst which, in turn, catalyzes ONPG formation. Such autocatalytic cycle can only operate by switching between high and low water activity conditions, such as in tidal pools cycling between wet and dry environments. Implications of the substrate-dependent formation of catalytically active peptides to prebiotic processes are discussed.

Original languageEnglish
Pages (from-to)369-382
Number of pages14
JournalOrigins of Life and Evolution of Biospheres
Volume35
Issue number4
DOIs
StatePublished - Aug 2005

Keywords

  • Anhydrous synthesis
  • Catalytic peptides
  • Iron
  • Prebiotic catalysis

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