Purification and separation of holo- and apo-forms of Saccharopolyspora erythraea acyl-carrier protein released from recombinant Escherichia coli by freezing and thawing

Saccharopolyspora erythraea acyl-carrier protein, highly expressed from a T7-based expression plasmid in Escherichia coli, can be selectively released from the cells in near-quantitative yield by a single cycle of freezing and thawing in a neutral buffer. Electrospray mass spectrometry was used to confirm that the recombinant S. erythraea acyl-carrier protein over-expressed in E. coli is present predominantly as the holo-form, with variable amounts of apo-acyl-carrier protein, holo-acyl-carrier protein dimer and holo-acyl-carrier protein glutathione adduct. The holo- and apo-acyl-carrier proteins are both readily purified on a large scale from the freeze-thaw extracts and can be separated from one another by octyl-Sepharose chromatography. The holo-acyl-carrier protein obtained in this way was fully active in supporting the synthesis of acyl-acyl-carrier protein by extracts of S. erythraea.