Determination of the X-Ray Crystallographic Structure of E.coli Butyryl-ACP

Abstract

Acyl Carrier Protein [ACP] is a small acidic protein which is an essential component of the type 2, dissociable fatty acid synthetase [1]. ACP is synthesised as an apo-protein and posttranslationally modified, by the addition of a 4’ phosphopantetheine [4’PANT] prosthetic group, which is linked to a serine residue by a phosphodiester bond. The amino acid sequence around the modified serine residue is highly conserved [2]. The post—translational modification is catalysed by holo-ACP synthetase [HAS], and this enzyme can also catalyse the direct conversion of apo-ACP to acyl-ACP using acyl-CoA as a source of the both the 4’ PANT and the acyl group [3]. Apart from the role of ACP in fatty acid biosynthesis it is an important component of a number of other reactions which require acyl-transferase steps, these include: membrane derived oligosaccharides, polyketide antibiotics, biotin precursor, and acyl-transfer to glycerol-3-phosphate [E.coli and plants] and lysophosphatidic acid. Additionally acyl-ACPs are the substrates for both thioesterases and soluble desaturases. NMR structures exist for holo-ACP and acyl-ACPs [4] and recently a X-ray crystallographic structure has been reported for a HAS-ACP complex from Bacillus subtilis [5]. In this study we are interested in determining the x-ray structure for an acyl-ACP and have used a combination of recombinant and non-recombinant proteins. Our eventual aim is to obtain structural data on a variety of different acyl-ACPs as well as acyl-ACP’ s complexed to enzymes of lipid metabolism.