Reexamination of the structural characteristics of the acyl carrier protein

Abstract

A secondary structure analysis of the acyl carrier protein (ACP) using circular dichroism (CD) spectroscopy has been carried out and compared with the nuclear magnetic resonance (NMR) results. This analysis gave a helix content of ∼ 60%, in good agreement with the NMR-determined value. As examined by CD, ACP was stable under varying conditions of protein concentration, pH, and ionic strength. ACP purified from an overproducing MR19 Escherichia coli strain was found to exist mostly as a dimer. Dimeric and monomeric fractions of ACP were separated using gel filtration chromatography. The ACP dimer was converted to the monomeric form by reduction, oxidation, and removal of the prosthetic group. The gel electrophoresis results indicated that the migration pattern of ACP is sensitive to specific conditions and that the “20-kDa” band does not always correspond to the ACP monomer with an anomalously low mobility but can represent a dimeric ACP species. Interestingly, both forms of ACP were biologically active, as shown by the ACP-dependent fatty acid synthase assay. The CD analysis of the ACP monomer and dimer yielded results indicative of conformational differences between these two forms of ACP. © 1997 John Wiley & Sons, Inc. Biospect 3: 171–181, 1997