Tsukamoto, Y. | bioRxiv Science

bioRxiv2022

Energy transfer in ubiquitous rhodopsin pumps with xanthophyll antennas

Energy transfer from light-harvesting ketocarotenoids to light-driven proton pumps xanthorhodopsins has been previously demonstrated in two unique cases: an extreme halophilic bacterium1 and a terrestrial cyanobacterium2. Attempts to find carotenoids that bind and transfer energy to rhodopsin proton pumps from the abundant marine and freshwater photoheterotrophs have thus far failed3-5. Here, using functional metagenomics combined with chromophore extraction from the environment, we detected light energy transfer from the widespread hydroxylated carotenoids zeaxanthin and lutein to the retinal moiety of xanthorhodopsins and proteorhodopsins. The light-harvesting carotenoids transfer up to 42% of the harvested energy in the violet/blue-light range to the green-light absorbing retinal chromophore. Our data suggest that these antennas have a significant impact on rhodopsin phototrophy in the worlds lakes, seas and oceans.

microbiology↗

bioRxiv2021

Comprehensive O-GlcNAc glycoproteomics on NOTCH1 EGF repeats refined sequons for O-GlcNAcylation and uncovered unique Lewis X epitopes in mammals

The O-GlcNAc modification of Notch receptors regulates Notch ligand interactions in a manner distinct from other forms of O-glycans on epidermal growth factor-like (EGF) repeats of Notch receptors. Although many proteins, besides Notch receptors, are expected to be O-GlcNAcylated by EGF domain-specific O-GlcNAc transferase (EOGT), only a small number of proteins have been reported to be modified in vivo, and elongated O-GlcNAc glycans have not been extensively explored. To extend our view of the specificity and variety of the glycan modification, we conducted a comprehensive analysis of O-GlcNAc glycans on NOTCH1 in mammals. Mass spectrometric analysis of NOTCH1 fragments expressed in HEK293T cells revealed that several EGF domains with putative O-GlcNAcylation sites were hardly modified with O-GlcNAc. Although amino acid residues before the modification site are preferentially occupied with aromatic residues, Phe and Tyr are preferable to Trp for the apparent modification with O-GlcNAc. Furthermore, a minor form of fucosylated O-GlcNAc glycans was detected in a subset of EGF domains. Fucosylation of O-GlcNAc glycans was enhanced by FUT1, FUT2, or FUT9 expression. The FUT9-dependent Lewis X epitope was confirmed by immunoblotting using an anti-Lewis X antibody. As expected from the similarity in the glycan structures, the Lexis X antigen was detected on O-fucose glycans. Our results refined the putative consensus sequence for the EOGT-dependent extracellular O-GlcNAc modification in mammals and revealed the structural diversity of functional Notch O-glycans.

biochemistry↗