Commutability of Bilin Chromophores in Plant Phytochromes

Commutability of Bilin Chromophores in Plant Phytochromes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Commutability of Bilin Chromophores in Plant Phytochromes Andreas Möglich, Chengwei Yi, David Golonka, Stefanie Meier, Kun Tang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6196749/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Organisms process environmental light conditions by sensory photoreceptors. In plants, phytochrome photoreceptors detect red and far-red light via covalently bound phytochromobilin (PФB) chromophores to regulate vital adaptive responses including shade avoidance and photomorphogenesis. By contrast, the chromophore of bacterial phytochromes (BphP) is biliverdin (BV), a ubiquitous bilin precursor to PФB biosynthesis. Covalent BV binding by plant phytochromes has not been reported, irrespective of the high structural conservation of the chromophore-binding pockets across the phytochrome superfamily. Unexpectedly, we now find plant phytochromes capable of autocatalytic BV incorporation via the same cysteine residue conventionally used for PФB attachment. BV-bound plant phytochromes retain full functionality as they undergo reversible photoconversion between their Pr and Pfr states and enter light-dependent interactions with downstream partners. BV incorporation into plant phytochromes is inherently inefficient but improves under far-red light and upon introduction of a histidine acting as an acid-base catalyst. Despite these advances, the heterologous deployment of BV-binding plant phytochromes in mammalian cells for optogenetics remains challenging. The chromophore promiscuity evidenced in plant phytochromes extends to BphPs and enables replacing BV by phycocyanobilin (PCB). Bound to PCB, a BphP-based optogenetic circuit retained full functionality but exhibited sensitivity to shorter wavelengths which may benefit application. Our work uncovers an unappreciated commutability of bilin chromophores in the phytochrome superfamily. The position of the active-site cysteine to which the bilin attaches emerges as the major, if not sole, driver for chromophore specificity. Biological sciences/Chemical biology/Synthetic biology Biological sciences/Plant sciences/Plant signalling bilin optogenetics photobiology phytochrome plant physiology sensory photoreceptor signal transduction tetrapyrrole Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6196749","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":431036210,"identity":"19d1ed95-c1f2-47a6-a1d4-96e02bb4fa15","order_by":0,"name":"Andreas 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In plants, phytochrome photoreceptors detect red and far-red light via covalently bound phytochromobilin (PФB) chromophores to regulate vital adaptive responses including shade avoidance and photomorphogenesis. By contrast, the chromophore of bacterial phytochromes (BphP) is biliverdin (BV), a ubiquitous bilin precursor to PФB biosynthesis. Covalent BV binding by plant phytochromes has not been reported, irrespective of the high structural conservation of the chromophore-binding pockets across the phytochrome superfamily. Unexpectedly, we now find plant phytochromes capable of autocatalytic BV incorporation via the same cysteine residue conventionally used for PФB attachment. BV-bound plant phytochromes retain full functionality as they undergo reversible photoconversion between their Pr and Pfr states and enter light-dependent interactions with downstream partners. BV incorporation into plant phytochromes is inherently inefficient but improves under far-red light and upon introduction of a histidine acting as an acid-base catalyst. Despite these advances, the heterologous deployment of BV-binding plant phytochromes in mammalian cells for optogenetics remains challenging. The chromophore promiscuity evidenced in plant phytochromes extends to BphPs and enables replacing BV by phycocyanobilin (PCB). Bound to PCB, a BphP-based optogenetic circuit retained full functionality but exhibited sensitivity to shorter wavelengths which may benefit application. Our work uncovers an unappreciated commutability of bilin chromophores in the phytochrome superfamily. 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