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Olenginski GM, Piacentini J, Harris DR, Runko NA, Papoutsis BM, Alter JR, Hess KR, Brewer SH, Phillips-Piro CM. Structural and spectrophotometric investigation of two unnatural amino-acid altered chromophores in the superfolder green fluorescent protein. Acta Crystallogr D Struct Biol 2021; 77:1010-1018. [PMID: 34342274 PMCID: PMC8329867 DOI: 10.1107/s2059798321006525] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Accepted: 06/21/2021] [Indexed: 11/10/2022] Open
Abstract
The spectrophotometric properties of the green fluorescent protein (GFP) result from the post-translationally cyclized chromophore composed of three amino acids including a tyrosine at the center of the β-barrel protein. Altering the amino acids in the chromophore or the nearby region has resulted in numerous GFP variants with differing photophysical properties. To further examine the effect of small atomic changes in the chromophore on the structure and photophysical properties of GFP, the hydroxyl group of the chromophore tyrosine was replaced with a nitro or a cyano group. The structures and spectrophotometric properties of these superfolder GFP (sfGFP) variants with the unnatural amino acids (UAAs) 4-nitro-L-phenylalanine or 4-cyano-L-phenylalanine were explored. Notably, the characteristic 487 nm absorbance band of wild-type (wt) sfGFP is absent in both unnatural amino-acid-containing protein constructs (Tyr66pNO2Phe-sfGFP and Tyr66pCNPhe-sfGFP). Consequently, neither Tyr66pNO2Phe-sfGFP nor Tyr66pCNPhe-sfGFP exhibited the characteristic emission of wt sfGFP centered at 511 nm when excited at 487 nm. Tyr66pNO2Phe-sfGFP appeared orange due to an absorbance band centered at 406 nm that was not present in wt sfGFP, while Tyr66pCNPhe-sfGFP appeared colorless with an absorbance band centered at 365 nm. Mass spectrometry and X-ray crystallography confirmed the presence of a fully formed chromophore and no significant structural changes in either of these UAA-containing protein constructs, signaling that the change in the observed photophysical properties of the proteins is the result of the presence of the UAA in the chromophore.
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Affiliation(s)
- Gregory M. Olenginski
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
| | - Juliana Piacentini
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
| | - Darcy R. Harris
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
| | - Nicolette A. Runko
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
| | - Brianna M. Papoutsis
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
| | - Jordan R. Alter
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
| | - Kenneth R. Hess
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
| | - Scott H. Brewer
- Department of Chemistry, Franklin & Marshall College, PO Box 3003, Lancaster, PA 17604-3003, USA
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Maurici N, Savidge N, Lee BU, Brewer SH, Phillips-Piro CM. Crystal structures of green fluorescent protein with the unnatural amino acid 4-nitro-L-phenylalanine. Acta Crystallogr F Struct Biol Commun 2018; 74:650-655. [PMID: 30279317 PMCID: PMC6168768 DOI: 10.1107/s2053230x1801169x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 08/17/2018] [Indexed: 11/10/2022] Open
Abstract
The X-ray crystal structures of two superfolder green fluorescent protein (sfGFP) constructs containing a genetically incorporated spectroscopic reporter unnatural amino acid, 4-nitro-L-phenylalanine (pNO2F), at two unique sites in the protein have been determined. Amber codon-suppression methodology was used to site-specifically incorporate pNO2F at a solvent-accessible (Asp133) and a partially buried (Asn149) site in sfGFP. The Asp133pNO2F sfGFP construct crystallized with two molecules per asymmetric unit in space group P3221 and the crystal structure was refined to 2.05 Å resolution. Crystals of Asn149pNO2F sfGFP contained one molecule of sfGFP per asymmetric unit in space group P4122 and the structure was refined to 1.60 Å resolution. The alignment of Asp133pNO2F or Asn149pNO2F sfGFP with wild-type sfGFP resulted in small root-mean-square deviations, illustrating that these residues do not significantly alter the protein structure and supporting the use of pNO2F as an effective spectroscopic reporter of local protein structure and dynamics.
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Affiliation(s)
- Nicole Maurici
- Department of Chemistry, Franklin and Marshall College, PO Box 3003, Lancaster, PA 17604, USA
| | - Nicole Savidge
- Department of Chemistry, Franklin and Marshall College, PO Box 3003, Lancaster, PA 17604, USA
| | - Byung Uk Lee
- Department of Chemistry, Franklin and Marshall College, PO Box 3003, Lancaster, PA 17604, USA
| | - Scott H. Brewer
- Department of Chemistry, Franklin and Marshall College, PO Box 3003, Lancaster, PA 17604, USA
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