title: Temperature effects on the allosteric responses of native and chimeric aspartate transcarbamoylases.
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.
authors.affiliation: College Station, The Texas A&M University System, TX 77843-2128, USA.
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: M E
authors.initials: ME
authors.lastname: Wales
authors.forename: J R
authors.initials: JR
authors.lastname: Wild
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000494:Allosteric Regulation / Q000187:drug effects; D000495:Allosteric Site; D000595:Amino Acid Sequence; D001221:Aspartate Carbamoyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism; D003570:Cytidine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D019281:Dimerization; D004789:Enzyme Activation / Q000187:drug effects; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D020035:Holoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012706:Serratia marcescens / Q000201:enzymology* / Q000235:genetics; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics; D014544:Uridine Triphosphate / Q000494:pharmacology; D015032:Zinc / Q000378:metabolism
chemical_list: D020035:Holoenzymes; D011993:Recombinant Fusion Proteins; D001224:Aspartic Acid; D003570:Cytidine Triphosphate; D000255:Adenosine Triphosphate; D001221:Aspartate Carbamoyltransferase; D015032:Zinc; D014544:Uridine Triphosphate