3cpa: Difference between revisions

[[Image:3cpa.jpg|left|200px]]<br /><applet load="3cpa" size="350" color="white" frame="true" align="right" spinBox="true"  

A high-resolution x-ray crystallographic investigation of the complex between carboxypeptidase A (CPA; peptidyl-L-amino-acid hydrolase, EC 3.4.17.1) and the slowly hydrolyzed substrate glycyl-L-tyrosine was done at -9 degrees C. Although this enzyme-substrate complex has been the subject of earlier crystallographic investigation, a higher resolution electron-density map of the complex with greater occupancy of the substrate was desired. All crystal chemistry (i.e., crystal soaking and x-ray data collection) was performed on a diffractometer-mounted flow cell, in which the crystal was immobilized. The x-ray data to 1.6-A resolution have yielded a well-resolved structure in which the zinc ion of the active site is five-coordinate: three enzyme residues (glutamate-72, histidine-69, and histidine-196) and the carbonyl oxygen and amino terminus of glycyl-L-tyrosine complete the coordination polyhedron of the metal. These results confirm that this substrate may be bound in a nonproductive manner, because the hydrolytically important zinc-bound water has been displaced and excluded from the active site. It is likely that all dipeptide substrates of carboxypeptidase A that carry an unprotected amino terminus are poor substrates because of such favorable bidentate coordination to the metal ion of the active site.

3CPA is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/ ] with <scene name='pdbligand=ZN:'>ZN</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. This structure supersedes the now removed PDB entry 1CPA. Active as [http://en.wikipedia.org/wiki/Carboxypeptidase_A Carboxypeptidase A], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.4.17.1 3.4.17.1] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=3CPA OCA].  

[[Category: Lipscomb, W N.]]

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