1ml4
From Proteopedia
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The PALA-liganded Aspartate transcarbamoylase catalytic subunit from Pyrococcus abyssi
Overview
The Pyrococcus abyssi aspartate transcarbamylase (ATCase) shows a high, degree of structural conservation with respect to the well-studied, mesophilic Escherichia coli ATCase, including the association of catalytic, and regulatory subunits. The adaptation of its catalytic function to high, temperature was investigated, using enzyme purified from recombinant, E.coli cells. At 90 degrees C, the activity of the trimeric catalytic, subunit was shown to be intrinsically thermostable. Significant extrinsic, stabilization by phosphate, a product of the reaction, was observed when, the temperature was raised to 98 degrees C. Comparison with the holoenzyme, showed that association with regulatory subunits further increases, thermostability. To provide further insight into the mechanisms of its, adaptation to high temperature, the crystal structure of the catalytic, subunit liganded with the analogue N-phosphonacetyl-L-aspartate (PALA) was, solved to 1.8A resolution and compared to that of the PALA-liganded, catalytic subunit from E.coli. Interactions with PALA are strictly, conserved. This, together with the similar activation energies calculated, for the two proteins, suggests that the reaction mechanism of the P.abyssi, catalytic subunit is similar to that of the E.coli subunit. Several, structural elements potentially contributing to thermostability were, identified: (i) a marked decrease in the number of thermolabile residues;, (ii) an increased number of charged residues and a concomitant increase of, salt links at the interface between the monomers, as well as the formation, of an ion-pair network at the protein surface; (iii) the shortening of, three loops and the shortening of the N and C termini. Other known, thermostabilizing devices such as increased packing density or reduction, of cavity volumes do not appear to contribute to the high thermostability, of the P.abyssi enzyme.
About this Structure
1ML4 is a Single protein structure of sequence from Pyrococcus abyssi with PAL as ligand. Active as Aspartate carbamoyltransferase, with EC number 2.1.3.2 Full crystallographic information is available from OCA.
Reference
Aspartate transcarbamylase from the hyperthermophilic archaeon Pyrococcus abyssi: thermostability and 1.8A resolution crystal structure of the catalytic subunit complexed with the bisubstrate analogue N-phosphonacetyl-L-aspartate., Van Boxstael S, Cunin R, Khan S, Maes D, J Mol Biol. 2003 Feb 7;326(1):203-16. PMID:12547202
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