1yca
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(New page: 200px<br /><applet load="1yca" size="450" color="white" frame="true" align="right" spinBox="true" caption="1yca, resolution 2.9Å" /> '''DISTAL POCKET POLARIT...)
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Revision as of 04:33, 21 November 2007
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DISTAL POCKET POLARITY IN LIGAND BINDING TO MYOGLOBIN: DEOXY AND CARBONMONOXY FORMS OF A THREONINE68 (E11) MUTANT INVESTIGATED BY X-RAY CRYSTALLOGRAPHY AND INFRARED SPECTROSCOPY
Overview
The crystal structures of the deoxy and carbonmonoxy forms of a distal, pocket myoglobin mutant in which valine68(E11) is replaced by threonine, have been solved to 2.1- and 2.2-A resolution, respectively. This, substitution has been shown previously to cause large decreases in the, rate of oxygen binding and to lower the equilibrium association constants, for O2 and CO. The synchrotron Laue method was used for the rapid, acquisition of X-ray diffraction data to overcome problems caused by the, very rapid rate of autooxidation of the mutant protein. The refined deoxy, structure shows that the noncoordinated water molecule in the distal, pocket is in a position to form strong hydrogen bonds with both the N, epsilon-H of the distal histidine64 and O gamma of threonine68 with no, other unexpected alterations in the protein structure. In the carbonmonoxy, form, the bound ligand is well-defined and inclined away from the two, hydrogen-bonding groups, refining to a position in which the Fe-C-O angle, is 162 degrees. This value is very close to that previously observed in, recombinant wild-type and position-64 (E7) mutants of sperm whale, myoglobin (160-170 degrees). The similarity of the CO conformations, contrasts with the 150-fold range in equilibrium binding constants (KCO), among the distal pocket myoglobin mutants and indicates that CO affinities, cannot be predicted from the coordination geometry of the bound ligand., Furthermore, a comparison of the infrared stretching frequencies of CO in, wild-type, valine64 and threonine68 single mutant, and, valine64-threonine68 double mutant pig carbonmonoxymyoglobins shows a lack, of correlation between KCO and vCO. These effects can be understood in, terms of the stability of noncovalently bound water in deoxymyoglobin and, electrostatic interactions between bound ligands and the distal pocket, residues.
About this Structure
1YCA is a Single protein structure of sequence from Sus scrofa with HEM and CMO as ligands. Full crystallographic information is available from OCA.
Reference
Distal pocket polarity in ligand binding to myoglobin: deoxy and carbonmonoxy forms of a threonine68(E11) mutant investigated by X-ray crystallography and infrared spectroscopy., Cameron AD, Smerdon SJ, Wilkinson AJ, Habash J, Helliwell JR, Li T, Olson JS, Biochemistry. 1993 Dec 7;32(48):13061-70. PMID:8241160
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