1s4v
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(New page: 200px<br /><applet load="1s4v" size="450" color="white" frame="true" align="right" spinBox="true" caption="1s4v, resolution 2.00Å" /> '''The 2.0 A crystal st...)
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Revision as of 23:59, 20 November 2007
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The 2.0 A crystal structure of the KDEL-tailed cysteine endopeptidase functioning in programmed cell death of Ricinus communis endosperm
Overview
In the senescing endosperm of germinating castor bean (Ricinus communis) a, special organelle (the ricinosome) releases a papain-type cysteine, endopeptidase (CysEP) during the final stages of cellular disintegration., Protein cleavage sites for the Ricinus CysEP were determined with, fluorogenic peptides (Abz-Xaa-Arg-/-Gln-Gln-Tyr(NO2)-Asp). The highest, kcat/Km values were obtained with neutral amino acid residues with large, aliphatic and non-polar (Leu, Val, Ile, Met) or aromatic (Phe, Tyr, Trp), side-chains. A second series (Abz-Leu-Xaa-/Gln-Pro-Tyr(NO2)-Asp) was, evaluated. Based on these results, the covalent binding inhibitor, H-D-Val-Leu-Lys-chloromethylketone (CMK) was chosen as substrate analogue, for replacement in the catalytic site. Unusually, CysEP cleaved, beta-casein N and C-terminal to the amino acid proline. CysEP was, crystallized, its structure was solved by molecular replacement at 2.0 A, resolution and refined to a R-factor of 18.1% (Rfree=22.6%). The, polypeptide chain folds as in papain into two domains divided by the, active site cleft, an elongated surface depression harboring the active, site. The non-primed specificity subsites of the proteinase are clearly, defined by the H-D-Val-Leu-Lys-CMK-inhibitor covalently bound to the, active site. The absence of the occluding loop, which blocks the active, site of exopeptidases at the C-terminal side of the scissile bond, identifies CysEP as an endopeptidase. The more open pocket of the Ricinus, CysEP correlates with the extended variety of substrate amino acid, residues accommodated by this enzyme, including even proline at the P1 and, P1' positions. This may allow the enzyme to attack a greater variety of, proteins during programmed cell death.
About this Structure
1S4V is a Single protein structure of sequence from Ricinus communis with SO4 as ligand. Full crystallographic information is available from OCA.
Reference
The 2.0 A crystal structure and substrate specificity of the KDEL-tailed cysteine endopeptidase functioning in programmed cell death of Ricinus communis endosperm., Than ME, Helm M, Simpson DJ, Lottspeich F, Huber R, Gietl C, J Mol Biol. 2004 Mar 5;336(5):1103-16. PMID:15037072
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