1es9
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(New page: 200px<br /><applet load="1es9" size="450" color="white" frame="true" align="right" spinBox="true" caption="1es9, resolution 1.3Å" /> '''X-RAY CRYSTAL STRUCTU...)
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Revision as of 12:09, 20 November 2007
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X-RAY CRYSTAL STRUCTURE OF R22K MUTANT OF THE MAMMALIAN BRAIN PLATELET-ACTIVATING FACTOR ACETYLHYDROLASES (PAF-AH)
Overview
The mammalian brain contains significant amounts of the cytosolic isoform, Ib of the platelet-activating factor acetylhydrolase (PAF-AH), a unique, type of PLA2. This oligomeric protein complex contains three types of, subunits: two homologous (63% identity) 26 kDa catalytic subunits, (alpha(1) and alpha(2)) which harbor all the PAF-AH activity, and the 45, kDa beta-subunit (LIS1), a product of the causal gene for Miller-Dieker, lissencephaly. During fetal development, the preferentially expressed, alpha(1)-subunit forms a homodimer, which binds to a homodimer of LIS1, whereas in adult organisms alpha(1)/alpha(2) and alpha(2)/alpha(2) dimers, also bound to dimeric LIS1, are the prevailing species. The consequences, of this "switching" are not understood, but appear to be of physiological, significance. The alpha(1)- and alpha(2)-subunits readily associate with, very high affinity to form homodimers. The nature of the interface has, been elucidated by the 1.7 A resolution crystal structure of the, alpha(1)/alpha(1) homodimer (Ho et al., 1997). Here, we examined the, functional consequences of the dimerization in both types of, alpha-subunits. We obtained monomeric protein in the presence of high, concentrations (>50 mM) of Ca2+ ions, and we show that it is catalytically, inactive and less stable than the wild type. We further show that Arg29, and Arg22 in one monomer contribute to the catalytic competence of the, active site across the dimer interface, and complement the catalytic triad, of Ser47, Asp192 and His195, in the second monomer. These results indicate, that the brain PAF-acetylhydrolase is a unique PLA2 in which dimerization, is essential for both stability and catalytic activity.
About this Structure
1ES9 is a Single protein structure of sequence from Bos taurus. Active as 1-alkyl-2-acetylglycerophosphocholine esterase, with EC number 3.1.1.47 Full crystallographic information is available from OCA.
Reference
The functional implications of the dimerization of the catalytic subunits of the mammalian brain platelet-activating factor acetylhydrolase (Ib)., McMullen TW, Li J, Sheffield PJ, Aoki J, Martin TW, Arai H, Inoue K, Derewenda ZS, Protein Eng. 2000 Dec;13(12):865-71. PMID:11239086
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