1k7w
From Proteopedia
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Crystal Structure of S283A Duck Delta 2 Crystallin Mutant
Overview
The major soluble avian eye lens protein, delta crystallin, is highly, homologous to the housekeeping enzyme argininosuccinate lyase (ASL). ASL, is part of the urea and arginine-citrulline cycles and catalyzes the, reversible breakdown of argininosuccinate to arginine and fumarate. In, duck lenses, there are two delta crystallin isoforms that are 94%, identical in amino acid sequence. Only the delta2 isoform has maintained, ASL activity and has been used to investigate the enzymatic mechanism of, ASL. The role of the active site residues Ser-29, Asp-33, Asp-89, Asn-116, Thr-161, His-162, Arg-238, Thr-281, Ser-283, Asn-291, Asp-293, Glu-296, Lys-325, Asp-330, and Lys-331 have been investigated by site-directed, mutagenesis, and the structure of the inactive duck delta2 crystallin, (ddeltac2) mutant S283A with bound argininosuccinate was determined at, 1.96 A resolution. The S283A mutation does not interfere with substrate, binding, because the 280's loop (residues 270-290) is in the open, conformation and Ala-283 is more than 7 A from the substrate. The, substrate is bound in a different conformation to that observed previously, indicating a large degree of conformational flexibility in the fumarate, moiety when the 280's loop is in the open conformation. The structure of, the S283A ddeltac2 mutant and mutagenesis results reveal that a complex, network of interactions of both protein residues and water molecules are, involved in substrate binding and specificity. Small changes even to, residues not involved directly in anchoring the argininosuccinate have a, significant effect on catalysis. The results suggest that either His-162, or Thr-161 are responsible for proton abstraction and reinforce the, putative role of Ser-283 as the catalytic acid, although we cannot, eliminate the possibility that arginine is released in an uncharged form, with the solvent providing the required proton. A detailed enzymatic, mechanism of ASL/ddeltac2 is presented.
About this Structure
1K7W is a Single protein structure of sequence from Anas platyrhynchos with AS1 as ligand. Active as Argininosuccinate lyase, with EC number 4.3.2.1 Full crystallographic information is available from OCA.
Reference
Mutational analysis of duck delta 2 crystallin and the structure of an inactive mutant with bound substrate provide insight into the enzymatic mechanism of argininosuccinate lyase., Sampaleanu LM, Yu B, Howell PL, J Biol Chem. 2002 Feb 8;277(6):4166-75. Epub 2001 Nov 6. PMID:11698398
Page seeded by OCA on Tue Nov 20 18:55:53 2007
