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Structure of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form.

ABSTRACT: Crystals of the catalytic subunit of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form contain four crystallographically independent trimers which associate in pairs to form stable staggered complexes that are similar to each other and to a previously determined monoclinic C2 form. Each subunit has a sulfate in the central channel. The catalytic subunits in these complexes show flexibility, with the elbow angles of the monomers differing by up to 7.4 degrees between crystal forms. Moreover, there is also flexibility in the relative orientation of the trimers around their threefold axis in the complexes, with a difference of 4 degrees between crystal forms.

SUBMITTER: Vitali J

PROVIDER: S-EPMC2531265 | biostudies-literature | 2008 Sep

REPOSITORIES: biostudies-literature

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Structure of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form.

Vitali Jacqueline J Colaneri Michael J MJ

Acta crystallographica. Section F, Structural biology and crystallization communications 20080820 Pt 9

Crystals of the catalytic subunit of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form contain four crystallographically independent trimers which associate in pairs to form stable staggered complexes that are similar to each other and to a previously determined monoclinic C2 form. Each subunit has a sulfate in the central channel. The catalytic subunits in these complexes show flexibility, with the elbow angles of the monomers differing by up to 7.4 degrees be ...[more]

PMID: 18765902

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Project description:Enzymes catalyze a particular reaction in cells, but only a few control the rate of this reaction and the metabolic pathway that follows. One specific mechanism for such enzymatic control of a metabolic pathway involves molecular feedback, whereby a metabolite further down the pathway acts at a unique site on the control enzyme to alter its activity allosterically. This regulation may be positive or negative (or both), depending upon the particular system. Another method of enzymatic control involves the cooperative binding of the substrate, which allows a large change in enzyme activity to emanate from only a small change in substrate concentration. Allosteric regulation and homotropic cooperativity are often known to involve significant conformational changes in the structure of the protein. Escherichia coli aspartate transcarbamoylase (ATCase) is the textbook example of an enzyme that regulates a metabolic pathway, namely, pyrimidine nucleotide biosynthesis, by feedback control and by the cooperative binding of the substrate, L-aspartate. The catalytic and regulatory mechanisms of this enzyme have been extensively studied. A series of X-ray crystal structures of the enzyme in the presence and absence of substrates, products, and analogues have provided details, at the molecular level, of the conformational changes that the enzyme undergoes as it shifts between its low-activity, low-affinity form (T state) to its high-activity, high-affinity form (R state). These structural data provide insights into not only how this enzyme catalyzes the reaction between l-aspartate and carbamoyl phosphate to form N-carbamoyl-L-aspartate and inorganic phosphate, but also how the allosteric effectors modulate this activity. In this Account, we summarize studies on the structure of the enzyme and describe how these structural data provide insights into the catalytic and regulatory mechanisms of the enzyme. The ATCase-catalyzed reaction is regulated by nucleotide binding some 60 Å from the active site, inducing structural alterations that modulate catalytic activity. The delineation of the structure and function in this particular model system will help in understanding the molecular basis of cooperativity and allosteric regulation in other systems as well.

Dataset Information

Structure of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form.

Publications

Structure of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form.

Similar Datasets

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