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| {{STRUCTURE_1ek4| PDB=1ek4 | SCENE= }} | | {{STRUCTURE_1ek4| PDB=1ek4 | SCENE= }} |
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| '''BETA-KETOACYL [ACYL CARRIER PROTEIN] SYNTHASE I IN COMPLEX WITH DODECANOIC ACID TO 1.85 RESOLUTION'''
| | ===BETA-KETOACYL [ACYL CARRIER PROTEIN] SYNTHASE I IN COMPLEX WITH DODECANOIC ACID TO 1.85 RESOLUTION=== |
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| ==Overview==
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| BACKGROUND: beta-ketoacyl-acyl carrier protein synthase (KAS) I is vital for the construction of the unsaturated fatty acid carbon skeletons characterizing E. coli membrane lipids. The new carbon-carbon bonds are created by KAS I in a Claisen condensation performed in a three-step enzymatic reaction. KAS I belongs to the thiolase fold enzymes, of which structures are known for five other enzymes. RESULTS: Structures of the catalytic Cys-Ser KAS I mutant with covalently bound C10 and C12 acyl substrates have been determined to 2.40 and 1.85 A resolution, respectively. The KAS I dimer is not changed by the formation of the complexes but reveals an asymmetric binding of the two substrates bound to the dimer. A detailed model is proposed for the catalysis of KAS I. Of the two histidines required for decarboxylation, one donates a hydrogen bond to the malonyl thioester oxo group, and the other abstracts a proton from the leaving group. CONCLUSIONS: The same mechanism is proposed for KAS II, which also has a Cys-His-His active site triad. Comparison to the active site architectures of other thiolase fold enzymes carrying out a decarboxylation step suggests that chalcone synthase and KAS III with Cys-His-Asn triads use another mechanism in which both the histidine and the asparagine interact with the thioester oxo group. The acyl binding pockets of KAS I and KAS II are so similar that they alone cannot provide the basis for their differences in substrate specificity.
| | The line below this paragraph, {{ABSTRACT_PUBMED_11286890}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 11286890 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_11286890}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Fatty acid synthase]] | | [[Category: Fatty acid synthase]] |
| [[Category: Thiolase fold]] | | [[Category: Thiolase fold]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 15:12:07 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 1 00:52:40 2008'' |
