Solution structure of B-subtilis acyl carrier protein

Background: Acyl carrier protein (ACP) is a fundamental component of fatty acid biosynthesis in which the fatty acid chain is elongated by the fatty a cid synthetase system while attached to the 4 ' -phosphopantetheine prosthe tic group (4 ' -PP) of ACP. Activation of ACP is mediated by holo-acyl carr ier protein synthase (ACPS) when ACPS transfers the 4 ' -PP moiety from coe nzyme A (CoA) to Ser36 of apo-ACP. Both ACP and ACPS have been identified a s essential for E, coli viability and potential targets for development of antibiotics. Results: The solution structure of B. subtilis ACP (9 kDa) has been determi ned using two-dimensional and three-dimensional heteronuclear NMR spectrosc opy. A total of 22 structures were calculated by means of hybrid distance g eometry-simulated annealing using a total of 1050 experimental NMR restrain ts. The atomic rmsd about the mean coordinate positions for the 22 structur es is 0.45 +/- 0.08 Angstrom for the backbone atoms and 0.93 +/- 0.07 Angst rom for all atoms. The overall ACP structure consists of a four alpha -heli cal bundle in which 4 ' -PP is attached to the conserved Ser36 that is loca ted in alpha helix II. Conclusions: Structural data were collected for both the apo and hole forms of ACP that suggest that the two forms of ACP are essentially identical. C omparison of the published structures for E. coli ACP and actinorhodin poly ketide synthase acyl carrier protein (act apo-ACP) from Streptomyces coelic olor A3(2) with B. subtilis ACP indicates similar secondary structure eleme nts but an extremely large rmsd between the three ACP structures (>4.3 Angs trom). The structural difference between B. subtilis ACP and both E. coli a nd act apo-ACP is not attributed to an inherent difference in the proteins, but is probably a result of a limitation in the methodology available for the analysis for E. coli and act apo-ACP. Comparison of the structure of fr ee ACP with the bound form of ACP in the ACP-ACPS complex reveals a displac ement of helix II in the vicinity of Ser36. The induced perturbation of ACP by ACPS positions Ser36 proximal to coenzyme A and aligns the dipole of he lix II to initiate transfer of 4 ' -PP to ACP.