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Neofunctionalization within the Omp85 protein superfamily during chloroplast evolution

Journal article
Authors Mats H. Töpel
Qihua Ling
Paul Jarvis
Published in Plant Signaling and Behaviour
Volume 7
Issue 2
Pages 161-164
Publication year 2012
Published at Department of Biological and Environmental Sciences
Pages 161-164
Language en
Keywords Arabidopsis thaliana, OEP80, Omp85, Toc75, beta-barrel proteins, chloroplast protein import, neofunctionalization, plastids, protein transport
Subject categories Evolutionary Biology, Bioinformatics and Systems Biology, Molecular biology


The Toc75 and OEP80 proteins reside in the chloroplast outer envelope membrane. Both are members of the Omp85 superfamily of β-barrel proteins, and both are essential in Arabidopsis plants with important roles throughout development. Toc75 forms the translocation channel of the TOC complex, which is responsible for importing nucleus-encoded proteins into chloroplasts, while the function of OEP80 remains uncertain. Deficiency of Toc75 in plants that have artificially reduced OEP80 levels suggests that the latter may be involved in the biogenesis of β-barrel proteins, in similar fashion to Omp85-related proteins in other systems. To elucidate the evolutionary relationship between the two proteins, we conducted a phylogenetic analysis using 48 sequences from diverse species. This indicated that Toc75 and OEP80 belong to sister groups in the Omp85 superfamily, and originate from a gene duplication in an ancient eukaryotic organism > 1.2 billion years ago. Our analysis also supports the notion that the Toc75 family has undergone a phase of neofunctionalization to accommodate the organelle’s newly acquired need to import proteins.

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