Zlenko, D. V. | bioRxiv Science

bioRxiv2018

Spontaneous Resolution in Racemic Solutions of N-trifluoroacetylated α-aminoalcohols

The spontaneous resolution was observed in the racemic solution of N-trifluoroacetylated -aminoalcohol (TFAAA-6) in CCl4. In against other cases of the conglomerates formation, the TFAAA-6 forms highly anisometric crystalline structures (strings). Herewith, the spontaneous resolution was not observed in the racemic solution of TFAAA-5 in heptane, where the isometric precipitate was formed. The latter was also observed in the TFAAA-5 solutions in heptane with small enantiomeric excess (EE), down to 2%. With that, the homochiral strings formed in the TFAAA-5 solutions in heptane with larger EEs. In this case, the strings formed from the excess of one of the enantiomers remained in solution after precipitation of the racemic residual. This process leads to the enhancement of chiral polarization in systems close to racemic and can explain the chiral purity of the living cell.

biophysics↗

bioRxiv2016

Assembly of photoactive Orange Carotenoid Protein from its domains unravels a carotenoid shuttle mechanism

The Orange Carotenoid Protein (OCP) is indispensable for cyanobacterial photoprotection by quenching phycobilisome fluorescence upon photoconversion from the orange OCPO to the red OCPR form. Cyanobacterial genomes frequently harbor, besides genes for Orange Carotenoid Proteins (OCPs), several genes encoding homologs of OCPs N- or C-terminal domains (NTD, CTD). Unlike the well-studied NTD homologs, called Red Carotenoid Proteins (RCPs), the role of CTD homologs remains elusive. We show how OCP can be reassembled from its functional domains. Expression of Synechocystis OCP-CTD in carotenoid-producing Escherichia coli yielded violet-colored proteins, which, upon mixing with the RCP-apoprotein, produced an orange-like photoswitchable form that further photoconverted into a species spectroscopically indistinguishable from RCP, thus demonstrating a unique carotenoid shuttle mechanism. The CTD itself is a novel, dimeric carotenoid-binding protein, which effectively quenches singlet oxygen and interacts with the Fluorescence Recovery Protein, assigning physiological roles to CTD homologs and explaining the evolutionary process of OCP formation.\n\nOne Sentence SummaryThe C-domain of cyanobacterial OCP dimerizes, binds a carotenoid, and delivers it to the N-domain forming photoactive OCP.

biophysics↗