3CSU

CATALYTIC TRIMER OF ESCHERICHIA COLI ASPARTATE TRANSCARBAMOYLASE

Summary for 3CSU

• Entry DOI: 10.2210/pdb3csu/pdb
• Descriptor: PROTEIN (ASPARTATE CARBAMOYLTRANSFERASE), CALCIUM ION (3 entities in total)
• Functional Keywords: transferase (carbamoyl-p, aspartate)
• Biological source: Escherichia coli
• Total number of polymer chains: 3
• Total formula weight: 103091.47

Authors

Beernink, P.T.,Endrizzi, J.A.,Alber, T.,Schachman, H.K. (deposition date: 1999-04-22, release date: 1999-05-11, Last modification date: 2023-08-30)

Primary citation

Beernink, P.T.,Endrizzi, J.A.,Alber, T.,Schachman, H.K.
Assessment of the allosteric mechanism of aspartate transcarbamoylase based on the crystalline structure of the unregulated catalytic subunit.
Proc.Natl.Acad.Sci.USA, 96:5388-5393, 1999

PubMed Abstract: The lack of knowledge of the three-dimensional structure of the trimeric, catalytic (C) subunit of aspartate transcarbamoylase (ATCase) has impeded understanding of the allosteric regulation of this enzyme and left unresolved the mechanism by which the active, unregulated C trimers are inactivated on incorporation into the unliganded (taut or T state) holoenzyme. Surprisingly, the isolated C trimer, based on the 1.9-A crystal structure reported here, resembles more closely the trimers in the T state enzyme than in the holoenzyme:bisubstrate-analog complex, which has been considered as the active, relaxed (R) state enzyme. Unlike the C trimer in either the T state or bisubstrate-analog-bound holoenzyme, the isolated C trimer lacks 3-fold symmetry, and the active sites are partially disordered. The flexibility of the C trimer, contrasted to the highly constrained T state ATCase, suggests that regulation of the holoenzyme involves modulating the potential for conformational changes essential for catalysis. Large differences in structure between the active C trimer and the holoenzyme:bisubstrate-analog complex call into question the view that this complex represents the activated R state of ATCase.

PubMed: 10318893
DOI: 10.1073/pnas.96.10.5388

Experimental method

X-RAY DIFFRACTION (1.88 Å)