The structural basis of thermostability of proteins is of great scientific and biotechnological interest. Differences in the X-ray structues of orthologous proteins from hyperthermophilic and mesophilic organisms can indicate crucial stabilizing interactions. To this end the crystal structure of dimeric phosphoribosyl anthranilate isomerase from the hyperthermophile Thermotoga maritima (tPRAI) was determined using phases derived from the isomorphous replacement method and was refined at 2.0 A resolution. The comparison to the known 2.0 A structure of PRAI from Escherichia coli (ePRAI) shows that tPRAI has the complete TIM- or (beta alpha)8-barrel fold, whereas helix alpha5 in ePRAI is replaced by a loop. The subunits of tPRAI associate via the N-terminal faces of their central beta-barrels. Two long, symmetry-related loops that protrude reciprocally into cavities of the other subunit provide for multiple hydrophobic interactions. Moreover, the side chains of the N-terminal methionines and the C-terminal leucines of both subunits are immobilized in a hydrophobic cluster, and the number of salt bridges is increased in tPRAI. These features appear to be mainly responsible for the high thermostability of tPRAI. In contrast to other hyperthermostable enzymes, tPRAI at 25 degrees C is catalytically more efficient than ePRAI, mainly due to its small K(M) value for the substrate [Sterner, R., Kleemann, G. R., Szadkowski, H., Lustig, A., Hennig, M., & Kirschner, K. (1996) Protein Sci. 5, 2000-2008]. The increased number of hydrogen bonds between the phosphate ion and tPRAI compared to ePRAI could be responsible for this effect.
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Evidence ID | Analyze ID | Gene/Complex | Systematic Name/Complex Accession | Qualifier | Gene Ontology Term ID | Gene Ontology Term | Aspect | Annotation Extension | Evidence | Method | Source | Assigned On | Reference |
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Evidence ID | Analyze ID | Gene | Gene Systematic Name | Phenotype | Experiment Type | Experiment Type Category | Mutant Information | Strain Background | Chemical | Details | Reference |
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Evidence ID | Analyze ID | Gene | Gene Systematic Name | Disease Ontology Term | Disease Ontology Term ID | Qualifier | Evidence | Method | Source | Assigned On | Reference |
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Evidence ID | Analyze ID | Regulator | Regulator Systematic Name | Target | Target Systematic Name | Direction | Regulation of | Happens During | Regulator Type | Direction | Regulation Of | Happens During | Method | Evidence | Strain Background | Reference |
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Site | Modification | Modifier | Source | Reference |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Allele | Assay | Annotation | Action | Phenotype | SGA score | P-value | Source | Reference | Note |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Assay | Annotation | Action | Modification | Source | Reference | Note |
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Complement ID | Locus ID | Gene | Species | Gene ID | Strain background | Direction | Details | Source | Reference |
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Evidence ID | Analyze ID | Dataset | Description | Keywords | Number of Conditions | Reference |
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