2x30
Crystal structure of the r139n mutant of a bifunctional enzyme pria
Structural highlights
FunctionHIS4_STRCO Catalyzes the isomerization of the aminoaldose moiety of ProFAR to the aminoketose of PRFAR in the biosynthesis pathway for histidine and the isomerization of the aminoaldose PRA to the aminoketose CdRP in the biosynthsis pathway for tryptophan.[HAMAP-Rule:MF_01014] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedA good model to experimentally explore evolutionary hypothesis related to enzyme function is the ancient-like dual-substrate (betaalpha)(8) phosphoribosyl isomerase (PriA), which takes part in both histidine and tryptophan biosynthesis in Streptomyces coelicolor and related organisms. In this study, we determined the Michaelis - Menten enzyme kinetics for both isomerase activities in wild-type PriA from S. coelicolor, as well as in selected single-residue mono-functional mutants, identified after Escherichia coli in vivo complementation experiments. Structural and functional analyses of a hitherto unnoticed residue contained on the functionally important beta --> alpha loop 5, namely, Arg(139), which was postulated on structural grounds to be important for the dual-substrate specificity of PriA, is presented for the first time. Indeed, enzyme kinetics analyses done on the mutant variants PriA_Ser(81)Thr and PriA_Arg(139)Asn showed that these residues, which are contained on beta --> alpha loops and in close proximity to the N-terminal phosphate-binding site, are essential solely for the phosphoribosyl anthranilate isomerase activity of PriA. Moreover, analysis of the X-ray crystallographic structure of PriA_Arg(139)Asn elucidated at 1.95 A herein, strongly implicates the occurrence of conformational changes in this beta --> alpha loop as a major structural feature related to the evolution of the dual-substrate specificity of PriA. It is suggested that PriA has evolved by tuning a fine energetic balance that allows the sufficient degree of structural flexibility needed for accommodating two topologically dissimilar substrates - within a bifunctional and thus highly constrained active site - without compromising its structural stability. Identification and analysis of residues contained on beta --> alpha loops of the dual-substrate (betaalpha)(8) phosphoribosyl isomerase a (PriA) specific for its phosphoribosyl anthranilate isomerase activity.,Noda-Garcia L, Camacho-Zarco AR, Verdel-Aranda K, Wright H, Soberon X, Fulop V, Barona-Gomez F Protein Sci. 2010 Jan 11. PMID:20066665[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
| ||||||||||||||||||||
