Chromophore binding to two cysteines increases quantum yield of near-infrared fluorescent proteins

David Buhrke, Neslihan N. Tavraz, Daria Shcherbakova, Luisa Sauthof, Marcus Moldenhauer, Francisco Vélazquez Escobar, Vladislav Verkhusha, Peter Hildebrandt, Thomas Friedrich

Research output: Contribution to journalArticle

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Abstract

Phytochromes are red/far-red light sensing photoreceptors employing linear tetrapyrroles as chromophores, which are covalently bound to a cysteine (Cys) residue in the chromophore-binding domain (CBD, composed of a PAS and a GAF domain). Recently, near-infrared (NIR) fluorescent proteins (FPs) engineered from bacterial phytochromes binding biliverdin IXα (BV), such as the iRFP series, have become invaluable probes for multicolor fluorescence microscopy and in vivo imaging. However, all current NIR FPs suffer from relatively low brightness. Here, by combining biochemical, spectroscopic and resonance Raman (RR) assays, we purified and characterized an iRFP variant that contains a BV chromophore simultaneously bound to two cysteines. This protein with the unusual double-Cys attached BV showed the highest fluorescence quantum yield (FQY) of 16.6% reported for NIR FPs, whereas the initial iRFP appeared to be a mixture of species with a mean FQY of 11.1%. The purified protein was also characterized with 1.3-fold higher extinction coefficient that together with FQY resulted in almost two-fold brighter fluorescence than the original iRFP as isolated. This work shows that the high FQY of iRFPs with two cysteines is a direct consequence of the double attachment. The PAS-Cys, GAF-Cys and double-Cys attachment each entails distinct configurational constraints of the BV adduct, which can be identified by distinct RR spectroscopic features, i.e. the marker band including the C=C stretching coordinate of the ring A-B methine bridge, which was previously identified as being characteristic for rigid chromophore embedment and high FQY. Our findings can be used to rationally engineer iRFP variants with enhanced FQYs.

Original languageEnglish (US)
Article number1866
JournalScientific Reports
Volume9
Issue number1
DOIs
StatePublished - Dec 1 2019

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Cysteine
Biliverdine
Fluorescence
Proteins
Phytochrome
Tetrapyrroles
Bacterial Proteins
Light

ASJC Scopus subject areas

  • General

Cite this

Buhrke, D., Tavraz, N. N., Shcherbakova, D., Sauthof, L., Moldenhauer, M., Vélazquez Escobar, F., ... Friedrich, T. (2019). Chromophore binding to two cysteines increases quantum yield of near-infrared fluorescent proteins. Scientific Reports, 9(1), [1866]. https://doi.org/10.1038/s41598-018-38433-2

Chromophore binding to two cysteines increases quantum yield of near-infrared fluorescent proteins. / Buhrke, David; Tavraz, Neslihan N.; Shcherbakova, Daria; Sauthof, Luisa; Moldenhauer, Marcus; Vélazquez Escobar, Francisco; Verkhusha, Vladislav; Hildebrandt, Peter; Friedrich, Thomas.

In: Scientific Reports, Vol. 9, No. 1, 1866, 01.12.2019.

Research output: Contribution to journalArticle

Buhrke, D, Tavraz, NN, Shcherbakova, D, Sauthof, L, Moldenhauer, M, Vélazquez Escobar, F, Verkhusha, V, Hildebrandt, P & Friedrich, T 2019, 'Chromophore binding to two cysteines increases quantum yield of near-infrared fluorescent proteins', Scientific Reports, vol. 9, no. 1, 1866. https://doi.org/10.1038/s41598-018-38433-2
Buhrke, David ; Tavraz, Neslihan N. ; Shcherbakova, Daria ; Sauthof, Luisa ; Moldenhauer, Marcus ; Vélazquez Escobar, Francisco ; Verkhusha, Vladislav ; Hildebrandt, Peter ; Friedrich, Thomas. / Chromophore binding to two cysteines increases quantum yield of near-infrared fluorescent proteins. In: Scientific Reports. 2019 ; Vol. 9, No. 1.
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