Analysis of the initial 2Fo-Fc and difference electron density maps at each coenzyme binding site of the protein revealed the presence of two 3´,5´-ADP molecules instead of the CoA that was added during crystallization. One 3´,5´-ADP resembles the conformation of the ADP portion of CoA in the binary CoA-AcpS or 3´,5´-ADP-AcpS structures from the PDB. The position of the second 3´,5´-ADP has never been described before. Its unusual coordination depends in part on lattice packing and the high concentration of magnesium, which suggests two interesting questions. Is the position of the second ADP dictated by the chemistry of the AcpS-catalyzed reaction? Though presence of the second ADP in the vicinity of the active site is a crystallographic artifact, can it assist in the design of inhibitor(s)? The biological relevance of the second ADP should be further investigated.
One paper was published: Acta Crystallogr D Biol Crystallogr. 2012 Oct;68(Pt 10):1359-70.