Abstract
Omega-3 polyunsaturated fatty acids (PUFA) are produced in some unicellular organisms, such as marine gammaproteobacteria, myxobacteria, and thraustochytrids, by large enzyme complexes called PUFA synthases. These enzymatic complexes resemble bacterial antibiotic-producing proteins known as polyketide synthases (PKS). One of the PUFA synthase subunits is a conserved large protein (PfaA in marine proteobacteria) that contains three to nine tandem acyl carrier protein (ACP) domains as well as condensation and modification domains. In this work, a study of the PfaA architecture and its ability to initiate the synthesis by selecting malonyl units has been carried out. As a result, we have observed a self-acylation ability in tandem ACPs whose biochemical mechanism differ from the previously described for type II PKS. The acyltransferase domain of PfaA showed a high selectivity for malonyl-CoA that efficiently loads onto the ACPs domains. These results, together with the structural organization predicted for PfaA, suggest that this protein plays a key role at early stages of the anaerobic pathway of PUFA synthesis.
Highlights
Omega-3 polyunsaturated fatty acids (PUFA) are produced in some unicellular organisms, such as marine gammaproteobacteria, myxobacteria, and thraustochytrids, by large enzyme complexes called PUFA synthases
The fatty acid intermediates are held by the acyl carrier protein domains (ACP) that transfer them to the different catalytic domains
ACP has to be previously activated with a 4Ј-phosphopantetheine prosthetic group (PPT) that acts as a linkage between the ACP active serine and the acyl group [8]
Summary
Omega-3 polyunsaturated fatty acids (PUFA) are produced in some unicellular organisms, such as marine gammaproteobacteria, myxobacteria, and thraustochytrids, by large enzyme complexes called PUFA synthases. PfaD is predicted to contain a singular enoyl reductase (ER) domain [6], whereas PfaA, PfaB, and PfaC are multimodular proteins, each of them formed by a series of domains that show sequence and structural homology with the ones present in PKS and FAS systems. These domains can be classified into condensing and modifier motifs according to their predicted biochemical function [7]. PfaA shows a KS–AT condensing module at their N-terminal half, followed by the tandem ACPs and a KR–DH C-terminal domain [3]
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