Molecular properties of short chain acyl thioesters of acyl carrier protein

S-Acylated derivatives of the acyl carrier protein (ACP) of Escherichia coli were prepared by a specific chemical reaction. The properties of acetyl-ACP, butyryl-ACP, and hexanoyl-ACP were compared with those of long chain (greater than C8) acyl-ACPs. Acylation of ACP with long chain (greater than or equal to C8) acyl groups stabilizes the protein to alkaline pH-induced hydrodynamic expansion, the degree of stabilization being independent of acyl chain length (Rock, C. O., and Cronan, J. E., Jr. (1979) J. Biol. Chem. 254, 9778-9785). This was not true of the short chain length acyl-ACPs. We report that the C2, C4, and C6 acyl-ACPs showed a lower degree of stabilization (greater hydrodynamic radii) under alkaline conditions than the longer chain lengths. The degree of stabilization (assayed by polyacrylamide gel electrophoresis at pH 9.5) was a direct function of acyl chain length (C8 greater than C6 greater than C4 greater than C2 greater than ACP). Long chain (greater than C10) acyl-ACPs bind tightly to octyl-Sepharose whereas ACP does not bind. The strength of binding is a direct function of acyl chain length for C10 to C16 (Rock, C. O., and Garwin, J. L. (1979) J. Biol. Chem. 254, 7123-7128). In contrast to the result expected if the entire acyl chain was accessible, we report that neither acetyl-ACP nor butyryl-ACP binds to octyl-Sepharose. Moreover, both hexanoyl-ACP and octanoyl-ACP bind less tightly to octyl-Sepharose than expected from extrapolation of the data for the longer chain length acyl-ACPs. Both the pH stabilization data and the hydrophobic chromatographic data are interpreted as indicating the presence of an acyl chain binding site on ACP that binds the first 6 to 8 carbon atoms of the acyl chain.