Phylogenetic analysis of homologous fatty acid synthase and polyketide synthase involved in aflatoxin biosynthesis

Marina Marcet- Houben,Maria Cabré,José L Paternáin,Antoni Romeu

doi:10.6026/97320630003033

Abstract

The first two steps of aflatoxin biosynthesis are catalyzed by the HexA/B and by the Pks protein. The phylogenetic analysis clearly distinguished fungal HexA/B from FAS subunits and from other homologous proteins. The phylogenetic trees of the HexA and HexB set of proteins share the same clustering. Proteins involved in the synthesis of fatty acids or in the aflatoxin or sterigmatocystin biosynthesis cluster separately. The Pks phylogenetic tree also differentiates the aflatoxin-related polypeptide sequences from those of other kinds of secondary metabolism. The function of some of the A. flavus Pks homologues may be deduced from the phylogenetic analysis. The conserved sequence motifs of protein domains shared by HexA/B and Pks - namely, beta-polyketide synthase (KS), acetyl transferase (AT) and acyl carrier protein (ACP) - have been identified, and the HexA/B and Pks involved in aflatoxin biosynthesis have been distinguished from those involved in primary metabolism or other kinds of secondary metabolism.

Highlights

Aflatoxins, a group of polyketide-derived compounds [1], are toxic and carcinogenic secondary metabolites synthesised only by such Aspergillus species as Aspergillus flavus, Aspergillus parasiticus and Aspergillus nominus [2, 3]
The conserved sequence motifs of protein domains shared by HexA/B and Pks - namely, β-polyketide synthase (KS), acetyl transferase (AT) and acyl carrier protein (ACP) - have been identified, and the HexA/B and Pks involved in aflatoxin biosynthesis have been distinguished from those involved in primary metabolism or other kinds of secondary metabolism
As far as the structure of fungal fatty acid synthase (FAS) is concerned, the acyl carrier protein (ACP), the ketoacylreductase (KR) (E.C. 1.1.1.100) and the ketoacyl synthase (KS) (E.C. 2.3.1.41) domains are distributed in the α-chain; and the acetyl transferase domain (AT) (E.C. 2.1.3.39), the enoylreductase (ER) (E.C. 1.3.1.9), the dehydratase (DH) (E.C. 4.2.1.61) and the malonyl-ACP transferase (MPT) (E.C. 2.1.3.39) domains are distributed in the β-chain [8]

Summary

Background

Aflatoxins, a group of polyketide-derived compounds [1], are toxic and carcinogenic secondary metabolites synthesised only by such Aspergillus species as Aspergillus flavus, Aspergillus parasiticus and Aspergillus nominus [2, 3]. We belonged to organisms that had previously appeared in can deduce that these A. flavus and A. oryzae sequences are our analysis of the FAS proteins This is the case of one of the A. flavus Pks sequences (AFSG011713) This protein is clustered in a group of proteins that are involved in the synthesis of several pigments (Bikaverin, Aurofusarin and Conidial yellow pigment) (coloured in purple). The ACP domain is a shared domain between Pks and HexA clustered with this sequence we find another homologue and, they have the same function, there are of the Pks of aflatoxin biosynthesis for A. flavus differences between the two domains.

Comparison between the three conserved parts of the

Conserved patterns in the KS and AT protein domains