Acyl Carrier Protein (ACP) Import into Chloroplasts

Abstract

During the import of the precursor for the acyl carrier protein (ACP) into chloroplasts, apoACP is converted to holoACP by the attachment of a phosphopantetheine group transferred from coenzyme A (CoA) by a chloroplast holoACP synthase [Fernandez, M. and Lamppa, G. (1990) Acyl carrier protein import into chloroplasts does not require the phosphopantetheine: evidence for a chloroplast holoACP synthase, Plant Cell 2, 195–‐2061. Here it is shown that exogenous addition of CoA to intact chloroplasts in the import assay stimulates the conversion of apoACP to holoACP. If adenosine 3′,5′‐bisphosphate [Ado(3′,5′)P2], the byproduct of the transfer reaction, was also included the extent of conversion was greatly reduced. CoA has its effect after ACP precursor (pre‐ACP) import and proteolytic removal of the transit peptide, thus indicating that the chloroplast holoACP synthase resides in the stroma where fatty acid synthase is found. When Ado(3′,5′)P2 was added alone to the import assay, it inhibited the synthesis of holoACP. Inhibition of the conversion of apo‐ to holoACP with Ado(3′,5′)P2 made it possible to examine whether the holoform of preACP could be imported into chloroplasts. Pre‐apoACP was synthesized in Escherichia coli and shown to be competent for import in an ATP‐ and temperature‐dependent manner. A partially purified chloroplast holoACP synthase converted 60–90% of the pre‐apoACP to pre‐holoACP. Pre‐holoACP incubated with chloroplasts in the presence of Ado(3′,5′)P2 yielded >60% holoACP, whereas the control reaction with pre‐apoACP gave primarily apoACP. Hence the phosphopantetheine prosthetic group of ACP does not block precursor movement through the translocation apparatus of the chloroplast envelope.

A phosphopantetheinyl transferase that is essential for mitochondrial fatty acid biosynthesis

“…Distinguishing among these models for the phosphopantetheinylation of apo‐ACPs has been hampered by the fact that the enzymes that catalyze this activation reaction have not been isolated (Elhussein et al ., ; Post‐Beittenmiller et al ., ; Fernandez and Lamppa, , ; Yang et al ., ), and the genetic components that encode these functions have not been characterized. In this study we have functionally characterized an Arabidopsis mtPPT enzyme that is responsible for phosphopantetheinylating mtACP isoforms, and we have begun to distinguish among the various models for the phosphopantetheinylation of organelle‐targeted ACP isoforms.…”

The phosphopantetheinyl transferases: catalysis of a post-translational modification crucial for life

“…240, 241 However, later on, it was shown that both apo - and holo -ACP could be efficiently taken up by the chloroplast. 242, 243 …”

The Yeast HAL2 Nucleotidase Is an in Vivo Target of Salt Toxicity

“…Another metabolic reaction sensitive to PAP accumulation is the transfer of a phosphopantetheine group from CoA to the acyl carrier protein. PAP is a product of the reaction, and it strongly inhibits the enzyme holoacyl carrier protein synthase (27). The accumulation of nonfunctional apoacyl carrier protein will inhibit lipid metabolism, especially the acylation of snglycerol-3-phosphate (28).…”