Abstract:
:The active form of the animal fatty acid synthase (FAS) is a dimer of identical multifunctional polypeptides, each containing seven discrete functional domains, that cooperate to form two centers for palmitate synthesis. To assess the importance of domain cooperation across the subunit interface in the reaction mechanism, we have utilized a strategy based on complementation analysis in vitro of modified FASs carrying critical mutations in specific catalytic domains. Homodimeric FASs carrying the same mutation(s) in both subunits are unable to synthesize fatty acids. As predicted by the current head-to-tail model for the animal FAS, heterodimeric FASs formed between the acyl carrier protein (ACP) mutant and either the beta-ketoacyl synthase (KS) or malonyl/acetyltransferase (MAT) are active in palmitate synthesis, confirming that the KS and MAT domains can cooperate with the ACP domain of the opposite subunit. Contrary to this model however, heterodimeric FASs formed between the KS and MAT mutants, between a MAT, ACP double mutant, and a KS mutant, and between a KS, ACP double mutant, and a MAT mutant are also active in palmitate synthesis, indicating that the MAT and KS domains can also cooperate with the ACP domain of the same subunit. The results of this study reveal an unanticipated element of redundancy in the FAS reaction mechanism in that the amino-terminal KS and MAT domains can make functional contact with the penultimate carboxy-terminal ACP domain of either subunit. A revised model for the FAS is proposed in which the substrate loading and condensation reactions can be catalyzed either by one of the two subunits or by cooperation between domains across the subunit interface.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Joshi AK,Witkowski A,Smith Sdoi
10.1021/bi971886vsubject
Has Abstractpub_date
1998-02-24 00:00:00pages
2515-23issue
8eissn
0006-2960issn
1520-4995pii
bi971886vjournal_volume
37pub_type
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