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Wang Q, Byrnes LJ, Shui B, Röhrig UF, Singh A, Chudakov DM, Lukyanov S, Zipfel WR, Kotlikoff MI, Sondermann H. Molecular mechanism of a green-shifted, pH-dependent red fluorescent protein mKate variant. PLoS One 2011; 6:e23513. [PMID: 21887263 PMCID: PMC3161743 DOI: 10.1371/journal.pone.0023513] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Accepted: 07/19/2011] [Indexed: 12/21/2022] Open
Abstract
Fluorescent proteins that can switch between distinct colors have contributed significantly to modern biomedical imaging technologies and molecular cell biology. Here we report the identification and biochemical analysis of a green-shifted red fluorescent protein variant GmKate, produced by the introduction of two mutations into mKate. Although the mutations decrease the overall brightness of the protein, GmKate is subject to pH-dependent, reversible green-to-red color conversion. At physiological pH, GmKate absorbs blue light (445 nm) and emits green fluorescence (525 nm). At pH above 9.0, GmKate absorbs 598 nm light and emits 646 nm, far-red fluorescence, similar to its sequence homolog mNeptune. Based on optical spectra and crystal structures of GmKate in its green and red states, the reversible color transition is attributed to the different protonation states of the cis-chromophore, an interpretation that was confirmed by quantum chemical calculations. Crystal structures reveal potential hydrogen bond networks around the chromophore that may facilitate the protonation switch, and indicate a molecular basis for the unusual bathochromic shift observed at high pH. This study provides mechanistic insights into the color tuning of mKate variants, which may aid the development of green-to-red color-convertible fluorescent sensors, and suggests GmKate as a prototype of genetically encoded pH sensors for biological studies.
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Affiliation(s)
- Qi Wang
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
| | - Laura J. Byrnes
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
| | - Bo Shui
- Department of Biomedical Science, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
| | - Ute F. Röhrig
- Molecular Modeling Group, Ludwig Institute for Cancer Research and Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Avtar Singh
- Department of Biomedical Engineering, Cornell University, Ithaca, New York, United States of America
| | - Dmitriy M. Chudakov
- Shemiakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia
- Nizhny Novgorod State Medical Academy, Nizhny Novgorod, Russia
| | - Sergey Lukyanov
- Shemiakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia
- Nizhny Novgorod State Medical Academy, Nizhny Novgorod, Russia
| | - Warren R. Zipfel
- Department of Biomedical Engineering, Cornell University, Ithaca, New York, United States of America
| | - Michael I. Kotlikoff
- Department of Biomedical Science, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
| | - Holger Sondermann
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
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