PMID:9743634
| Citation |
Liu, L, Wales, ME and Wild, JR (1998) Temperature effects on the allosteric responses of native and chimeric aspartate transcarbamoylases. J. Mol. Biol. 282:891-901 |
|---|---|
| Abstract |
Although structurally very similar, the aspartate transcarbamoylases (ATCase) of Serratia marcescens and Escherichia coli have distinct allosteric regulatory patterns. It has been reported that a S. marcescens chimera, SM : rS5'ec, in which five divergent residues (r93 to r97) of the regulatory polypeptide were replaced with their Escherichia coli counterparts, possessed E. coli-like regulatory characteristics. The reverse chimera EC:rS5'sm, in which the same five residues of E. coli have been replaced with their S. marcescens counterpart, lost both heterotrophic and homotropic responses. These results indicate that the r93-r97 region is critical in defining the ATCase allosteric character. Molecular modeling of the regulatory polypeptides has suggested that the replacement of the S5' beta-strand resulted in disruption of the allosteric-zinc interface. However, the structure-function relationship could be indirect, and the disruption of the interface could influence allostery by altering the global energy of the enzyme. Studies of the temperature-sensitivity of the CTP response demonstrate that it is possible to convert CTP inhibition of the SM:rS5'ec chimera at high temperature to activation below 10 degreesC. Nonetheless, the temperature response of the native S. marcescens ATCase suggests a strong entropic effect that counteracts the CTP activation. Therefore, it is suggested that the entropy component of the coupling free energy plays a significant role in the determination of both the nature and magnitude of the allosteric effect in ATCase. |
| Links |
PubMed PMC3233763 Online version:10.1006/jmbi.1998.2054 |
| Keywords |
Adenosine Triphosphate/pharmacology; Allosteric Regulation/drug effects; Allosteric Site; Amino Acid Sequence; Aspartate Carbamoyltransferase/chemistry; Aspartate Carbamoyltransferase/genetics; Aspartate Carbamoyltransferase/metabolism; Aspartic Acid/metabolism; Cytidine Triphosphate/metabolism; Cytidine Triphosphate/pharmacology; Dimerization; Enzyme Activation/drug effects; Escherichia coli/enzymology; Escherichia coli/genetics; Holoenzymes/chemistry; Holoenzymes/genetics; Holoenzymes/metabolism; Kinetics; Models, Molecular; Protein Conformation; Protein Structure, Secondary/drug effects; Recombinant Fusion Proteins/chemistry; Recombinant Fusion Proteins/genetics; Recombinant Fusion Proteins/metabolism; Serratia marcescens/enzymology; Serratia marcescens/genetics; Structure-Activity Relationship; Temperature; Thermodynamics; Uridine Triphosphate/pharmacology; Zinc/metabolism |
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