O oxigênio poderia estar disponível para a vida tão cedo quanto 3.5 bilhões de anos atrás

quarta-feira, novembro 28, 2018

Early Archean origin of Photosystem II

Tanai Cardona, Patricia Sánchez‐Baracaldo, A. William Rutherford, Anthony W. Larkum

First published: 09 November 2018



Photosystem II is a photochemical reaction center that catalyzes the light‐driven oxidation of water to molecular oxygen. Water oxidation is the distinctive photochemical reaction that permitted the evolution of oxygenic photosynthesis and the eventual rise of eukaryotes. At what point during the history of life an ancestral photosystem evolved the capacity to oxidize water still remains unknown. Here, we study the evolution of the core reaction center proteins of Photosystem II using sequence and structural comparisons in combination with Bayesian relaxed molecular clocks. Our results indicate that a homodimeric photosystem with sufficient oxidizing power to split water had already appeared in the early Archean about a billion years before the most recent common ancestor of all described Cyanobacteria capable of oxygenic photosynthesis, and well before the diversification of some of the known groups of anoxygenic photosynthetic bacteria. Based on a structural and functional rationale, we hypothesize that this early Archean photosystem was capable of water oxidation to oxygen and had already evolved protection mechanisms against the formation of reactive oxygen species. This would place primordial forms of oxygenic photosynthesis at a very early stage in the evolutionary history of life.

Archean Chloroflexi Cyanobacteria evolution photosystem Proteobacteria 
reaction center water oxidation

Funding Information
Imperial College London
Leverhulme Trust. Grant Number: RPG‐2017‐223
Royal Society
Biotechnology and Biological Sciences Research Council. Grant Numbers: BB/K002627/1, BB/L011206/1

Publication History
Version of Record online: 09 November 2018
Manuscript accepted: 11 October 2018 Manuscript revised: 03 October 2018
Manuscript received: 13 September 2018