Shifting the Hydrolysis Equilibrium of Substrate Loaded Acyl Carrier Proteins.

Acyl carrier proteins (ACP)s transport intermediates through many primary and secondary metabolic pathways. Studying the effect of substrate identity on ACP structure has been hindered by the lability of the thioester bond that attaches acyl substrates to the 4'-phosphopantetheine cofactor of ACP. Here we show that an acyl acyl-carrier protein synthetase (AasS) can be used in real time to shift the hydrolysis equilibrium toward favoring acyl-ACP during solution NMR spectroscopy. Only 0.005 molar equivalents of AasS enables 1 week of stability to palmitoyl-AcpP from Escherichia coli. 2D NMR spectra enabled with this method revealed that the tethered palmitic acid perturbs nearly every secondary structural region of AcpP. This technique will allow previously unachievable structural studies of unstable acyl-ACP species, contributing to the understanding of these complex biosynthetic pathways.