title: Allosteric regulation in a family of enterobacterial aspartate transcarbamylases: intramolecular transmission of regulatory signals in chimeric enzymes.
abstract: Several enterobacterial aspartate transcarbamylases (ATCases) exhibit a [2(C3):3(r2)] quaternary structure analogous to that of the Escherichia coli enzyme. Despite their conserved quaternary structures, these enzymes present substantial differences in the co-operativity of substrate binding and in their allosteric regulation by nucleotide effectors. A comparison between different enzymatic species provides an opportunity to expand our understanding of the molecular basis of allostery in ATCase. Chimeric ATCases were constructed by exchanging subdomain regions involved in quaternary structural features, such as the r1-c4 regulatory-catalytic subunit interface analyzed in this study, in order to define the involvement of this interface in the several components of allosteric regulation. The r1-c4 interface was found to constitute an essential element for the recognition and the transmission of the ATP regulatory signal in the Serratia marcescens and the Proteus vulgaris ATCases, as it does in the E. coli ATCase. Besides, the specific amino acid composition of the C-terminal region of the regulatory chain and its interactions with the amino acid residues in the 240s loop of the catalytic chain (r1-c4 interactions) were found to modulate the amplitude of the enzyme's response to ATP. The C-terminal region of the regulatory chain did not appear to participate directly in the regulation of the three native ATCases by CTP. Even when CTP acts as an activator, as in the P. vulgaris and S. marcescens ATCases, its signal follows a route distinct from that of the general activator ATP. Synergistic inhibition by CTP and UTP was found to involve the transmission of a specific UTP signal. This signal appeared different in the various ATCases, involving the C-terminal region of the regulatory chain in the E. coli and S. marcescens ATCases but not in the P. vulgaris ATCase.
authors.affiliation: Laboratorium voor Erfelikheidsleer en Microbiologie, Vrije Universiteit Brussel, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Cunin
authors.forename: M E
authors.initials: ME
authors.lastname: Wales
authors.forename: F
authors.initials: F
authors.lastname: Van Vliet
authors.forename: C
authors.initials: C
authors.lastname: De Staercke
authors.forename: L
authors.initials: L
authors.lastname: Scapozza
authors.forename: C S
authors.initials: CS
authors.lastname: Rani
authors.forename: J R
authors.initials: JR
authors.lastname: Wild
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D001221:Aspartate Carbamoyltransferase / Q000737:chemistry* / Q000502:physiology; D017124:Conserved Sequence; D003570:Cytidine Triphosphate / Q000378:metabolism; D004755:Enterobacteriaceae / Q000201:enzymology*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D016415:Sequence Alignment; D015398:Signal Transduction; D014544:Uridine Triphosphate / Q000378:metabolism
chemical_list: D011993:Recombinant Fusion Proteins; D003570:Cytidine Triphosphate; D000255:Adenosine Triphosphate; D001221:Aspartate Carbamoyltransferase; D014544:Uridine Triphosphate