1myj
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(New page: 200px<br /><applet load="1myj" size="450" color="white" frame="true" align="right" spinBox="true" caption="1myj, resolution 1.9Å" /> '''DISTAL POLARITY IN LI...)
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Revision as of 19:41, 20 November 2007
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DISTAL POLARITY IN LIGAND BINDING TO MYOGLOBIN: STRUCTURAL AND FUNCTIONAL CHARACTERIZATION OF A THREONINE68(E11) MUTANT
Overview
Site-directed mutagenesis studies have confirmed that the distal histidine, in myoglobin stabilizes bound O2 by hydrogen bonding and have suggested, that it is the polar character of the imidazole side chain rather than its, size that limits the rate of ligand entry into the protein. We constructed, an isosteric Val68 to Thr replacement in pig myoglobin (i) to investigate, whether the O2 affinity could be increased by the introduction of a second, hydrogen-bonding group into the distal heme pocket and (ii) to examine the, influence of polarity on the ligand binding rates more rigorously. The, 1.9-A crystal structure of Thr68 aquometmyoglobin confirms that the mutant, and wild-type proteins are essentially isostructural and reveals that the, beta-OH group of Thr68 is in a position to form hydrogen-bonding, interactions both with the coordinated water molecule and with the main, chain greater than C=O of residue 64. The rate of azide binding to the, ferric form of the Thr68 mutant was 60-fold lower than that for the, wild-type protein, consistent with the proposed stabilization of the, coordinated water molecule. However, bound O2 is destabilized in the, ferrous form of the mutant protein. The observed 17-fold lowering of the, O2 affinity may be a consequence of the hydrogen-bonding interaction made, between the Thr68 beta-OH group and the carbonyl oxygen of residue 64., Overall association rate constants for O2, NO, and alkyl isocyanide, binding to ferrous pig myoglobin were 3-10-fold lower for the mutant, compared to the wild-type protein, whereas that for CO binding was little, affected.(ABSTRACT TRUNCATED AT 250 WORDS)
About this Structure
1MYJ is a Single protein structure of sequence from Sus scrofa with SO4 and HEM as ligands. Full crystallographic information is available from OCA.
Reference
Distal pocket polarity in ligand binding to myoglobin: structural and functional characterization of a threonine68(E11) mutant., Smerdon SJ, Dodson GG, Wilkinson AJ, Gibson QH, Blackmore RS, Biochemistry. 1991 Jun 25;30(25):6252-60. PMID:1905570
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