Illustration (IMAGE) Max-Planck-Gesellschaft Caption In a cyanobacterial phytoprotection system, The Fluorescence Recovery Protein (FRP) binds to activated Orange Carotenoid Protein OCP1 to restore its protective form. Ancestral protein sequence reconstruction shows that compatibility between FRP and OCP evolved independently in completely different species. Thus, when the proteins did encounter each other, they were a perfect match. In the photoprotective system of cyanobacteria, the Fluorescence Recovery Protein (FRP) binds to the activated Orange Carotenoid Protein OCP1 to restore its initial form. Through horizontal gene transfer (HGT), a process in which bacteria exchange genetic material, a precursor of the FRP protein was transferred into the cyanobacteria. Reconstruction of the original protein sequence shows that the mutual compatibility of FRP and OCP evolved independently in completely different microbial species. Interestingly, the FRP from proteobacteria could already interact with the OCP of cyanobacteria. The ability to bind to the interface of ancestral OCP (AncOCP) had already evolved by chance in proteobacteria. When the proteins first met, they were already perfectly matched. FRP now exploits a conserved dimerization interface of OCP to strongly control OCP1 paralogs allosterically. OCP structure used here for illustration only is 3MG1 (PDB ID). Credit Max Planck Institute for Terrestrial Microbiology/Hochberg Usage Restrictions Use of images is limited to editorial coverage of scientific topics relating to the activities of the Max Planck Society. Any kind of commercial use (including, in particular, the exploitation of images by means of sale or incorporation in image databases or image catalogues) as well as any promotional use/use for merchandise purposes, disclosure to third parties or granting of related rights to third parties is expressly not permitted. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.