Equilibrium and kinetic studies of the association of catalytic and regulatory subunits of aspartate transcarbamoylase.

Bothwell, Mark A.; Schachman, H. K.

doi:10.1016/s0021-9258(19)85977-x

Cited by 21 publications

(1 citation statement)

References 37 publications

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“…In fact, Glu-239 is located in the vicinity of the catalytic-regulatory interface (C-R) in the unliganded form (Honzatko et al, 1982;Ke et al, 1984), and the Glu-239 to Gin change could equally well disturb this interface, thereby destabilizing the T state. This is consistent with several reports emphasizing the involvement of the C-R interface in the homotropic cooperativity (Subranami et al, 1977;Bothwell & Schachman, 1980;Ladjimi et al, 1985;Chan, 1975a,b;Chan & Enns, 1981;Ladner et al, 1982).…”

Section: Discussionsupporting

confidence: 93%

A possible model for the concerted allosteric transition in Escherichia coli aspartate transcarbamylase as deduced from site-directed mutagenesis studies

Ladjimi¹,

Kantrowitz²

1988

Biochemistry

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Aspartate transcarbamylase is stabilized in a low-affinity-low-activity state exhibiting no cooperativity by selective perturbation of the Glu-50-Arg-167 and Glu-50-Arg-234 interdomain salt bridges. Similarly, a high-affinity-high-activity state of the enzyme, retaining a significant amount of cooperativity, is obtained by perturbation of the interaction between Tyr-240 and Asp-271. In this work, we show that the rupture of the link between Tyr-240 and Asp-271 in the enzyme already lacking the interdomain salt bridges regenerates the homotropic cooperative interactions between the catalytic sites and substantially increases the activity and affinity of the enzyme for aspartate. These results suggest a possible relationship between these two sets of interactions for the establishment of the cooperative behavior of the enzyme. Another mutation, Glu-239 to Gln, introduced to perturb the Glu-239-Lys-164 and Glu-239-Tyr-165 interactions between the two catalytic subunits, is sufficient to "lock" the enzyme in the R state. These observations emphasize the importance of the interactions at the interface between the catalytic trimers in maintaining the T state of the enzyme and shed light on the role played by this pathway in the communication of homotropic cooperativity between the different sites. A model including all these findings, as well as the interactions stabilizing the T state or the R state in the presence of the natural substrates, is proposed.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Discussionsupporting

confidence: 93%

A possible model for the concerted allosteric transition in Escherichia coli aspartate transcarbamylase as deduced from site-directed mutagenesis studies

Ladjimi¹,

Kantrowitz²

1988

Biochemistry

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Proteinfaltung und Proteinassoziation

Jaenicke

1984

Angewandte Chemie

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Die Biosynthese von Proteinen führt zu linearen Kettenmolekülen mit streng definierter Reihenfolge der Aminosäurebausteine. Diese ist aufgrund des genetischen Codes auf der Ebene der Nucleinsäure durch die Nucleotidsequenz des zugehörigen Gens festgelegt. Denaturierungs‐Renaturierungs‐Experimente legen die These nahe, die in der Polypeptidkette vorgegebene eindimensionale Information determiniere die dreidimensionale Struktur vollständig. Demnach sollte ein „Faltungscode”︁ existieren, der das spontane Zustandekommen der thermodynamisch stabilen „nativen”︁ Struktur bestimmt. Der Prozeß der Faltung (in vivo wie in vitro) ist trotz der astronomisch großen Zahl möglicher Konformationen ein schneller Vorgang. Der Faltungsmechanismus muß daher kinetisch kontrolliert sein. Die Frage, ob die native Struktur letztlich ein „lokales”︁ oder das „globale”︁ Minimum der Energiehyperfläche besetzt, bleibt offen. Oberhalb einer kritischen Molekülgröße liegen Proteine als Molekülassoziate vor. Die Einheitlichkeit der „Quartärstruktur”︁ setzt eine enge Korrelation von Faltung und Assoziation sowie Spezifität voraus; beides wird durch Rekonstitutionsexperimente in vitro bestätigt.

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Protein Folding and Protein Association

Jaenicke

1984

Angew. Chem. Int. Ed. Engl.

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The biosynthesis of proteins leads to linear chain1 molecules with a well-defined amino acid sequence that is unambiguously determined by a corresponding polynucleotide sequence at the level of the gene. The underlying mechanism of transcription and translation is based upon the complementarity of pyrimidine and purine bases, on the one hand, and the genetic code, on the other. As indicated by denaturationhenaturation experiments, the one-dimensional structural information encoded in the polypeptide chain generates a unique three-dimensional structure. In consequence, one would expect a "folding code" to exist which governs the spontaneous acquisition of the therrnodynamically stable "native" structure of a given protein. The rate of folding (in vivo as well as in vitro) is fast, despite the astronomically high number of potential conformations. Tlhe mechanism of folding must therefore be kinetically controlled. Whether the native structure represents the "global" or a "local" minimum on the energy hyperspace is an open question. Above a critical size, protein molecules tend to be organized as assemblies made up of identical or non-identical subunits. The observed uniformity of a given "quaternary structure" requires a close correlation of folding and association as well as a high specificity of subunit recognition. Both are corroborated by in vitro reconstitution experiments.

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Equilibrium and kinetic studies of the association of catalytic and regulatory subunits of aspartate transcarbamoylase.

Cited by 21 publications

References 37 publications

A possible model for the concerted allosteric transition in Escherichia coli aspartate transcarbamylase as deduced from site-directed mutagenesis studies

A possible model for the concerted allosteric transition in Escherichia coli aspartate transcarbamylase as deduced from site-directed mutagenesis studies

Proteinfaltung und Proteinassoziation

Protein Folding and Protein Association

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