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Simonson T, Ye-Lehmann S, Palmai Z, Amara N, Wydau-Dematteis S, Bigan E, Druart K, Moch C, Plateau P. Redesigning the stereospecificity of tyrosyl-tRNA synthetase. Proteins 2016; 84:240-53. [PMID: 26676967 DOI: 10.1002/prot.24972] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Revised: 09/30/2015] [Accepted: 11/26/2015] [Indexed: 12/14/2022]
Abstract
D-Amino acids are largely excluded from protein synthesis, yet they are of great interest in biotechnology. Unnatural amino acids have been introduced into proteins using engineered aminoacyl-tRNA synthetases (aaRSs), and this strategy might be applicable to D-amino acids. Several aaRSs can aminoacylate their tRNA with a D-amino acid; of these, tyrosyl-tRNA synthetase (TyrRS) has the weakest stereospecificity. We use computational protein design to suggest active site mutations in Escherichia coli TyrRS that could increase its D-Tyr binding further, relative to L-Tyr. The mutations selected all modify one or more sidechain charges in the Tyr binding pocket. We test their effect by probing the aminoacyl-adenylation reaction through pyrophosphate exchange experiments. We also perform extensive alchemical free energy simulations to obtain L-Tyr/D-Tyr binding free energy differences. Agreement with experiment is good, validating the structural models and detailed thermodynamic predictions the simulations provide. The TyrRS stereospecificity proves hard to engineer through charge-altering mutations in the first and second coordination shells of the Tyr ammonium group. Of six mutants tested, two are active towards D-Tyr; one of these has an inverted stereospecificity, with a large preference for D-Tyr. However, its activity is low. Evidently, the TyrRS stereospecificity is robust towards charge rearrangements near the ligand. Future design may have to consider more distant and/or electrically neutral target mutations, and possibly design for binding of the transition state, whose structure however can only be modeled.
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Affiliation(s)
- Thomas Simonson
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
| | | | - Zoltan Palmai
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
| | - Najette Amara
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
| | - Sandra Wydau-Dematteis
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
| | - Erwan Bigan
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
| | - Karen Druart
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
| | - Clara Moch
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
| | - Pierre Plateau
- Department of Biology, Laboratoire De Biochimie (CNRS UMR7654), Ecole Polytechnique, Palaiseau, 91128, France
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Kannan N, Chander P, Ghosh P, Vishveshwara S, Chatterji D. Stabilizing interactions in the dimer interface of alpha-subunit in Escherichia coli RNA polymerase: a graph spectral and point mutation study. Protein Sci 2001; 10:46-54. [PMID: 11266593 PMCID: PMC2249855 DOI: 10.1110/ps.26201] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Abstract
The formation of alpha(2) dimer in Escherichia coli core RNA polymerase (RNAP) is thought to be the first step toward the assembly of the functional enzyme. A large number of evidences indicate that the alpha-subunit dimerizes through its N-terminal domain (NTD). The crystal structures of the alpha-subunit NTD and that of a homologous Thermus aquaticus core RNAP are known. To identify the stabilizing interactions in the dimer interface of the alpha-NTD of E. coli RNAP, we identified side-chain clusters by using the crystal structure coordinates of E. coli alpha-NTD. A graph spectral algorithm was used to identify side-chain clusters. This algorithm considers the global nonbonded side-chain interactions of the residues for the clustering procedure and is unique in identifying residues that make the largest number of interactions among the residues that form clusters in a very quantitative way. By using this algorithm, a nine-residue cluster consisting of polar and hydrophobic residues was identified in the subunit interface adjacent to the hydrophobic core. The residues forming the cluster are relatively rigid regions of the interface, as measured by the thermal factors of the residues. Most of the cluster residues in the E. coli enzyme were topologically and sequentially conserved in the T. aquaticus RNAP crystal structure. Residues 35F and 46I were predicted to be important in the stability of the alpha-dimer interface, with 35F forming the center of the cluster. The predictions were tested by isolating single-point mutants alpha-F35A and alpha-I46S on the dimer interface, which were found to disrupt dimerization. Thus, the identified cluster at the edge of the dimer interface seems to be a vital component in stabilizing the alpha-NTD.
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Affiliation(s)
- N Kannan
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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