BIOCHEMISTRY Correction for “Mechanism of ligand-gated potassium efflux in bacterial pathogens,” by Tarmo P. Roosild, Samantha Castronovo, Jess Healy, Samantha Miller, Christos Pliotas, Tim Rasmussen, Wendy Bartlett, Stuart J. Conway, and Ian R. Booth, which appeared in issue 46, November 16, 2010, of Proc Natl Acad Sci USA (107:19784–19789; first published November 1, 2010; 10.1073/pnas.1012716107).
The undersigned authors wish to note, “The KefFC system of E. coli is maintained in an inactive state by the binding of glutathione (GSH) and is activated by the formation of GSH adducts (GSX), particularly those with bulky substituents. We described two crystal structures with density present in the ligand-binding domain that we interpreted as GSH and GSX. Recently, an independent, experienced crystallographer, who had viewed the structures from our study in a different context, made representations to us that cast doubt on position of the succinimido ring of GSX. We have further reviewed the density maps with the aid of an experienced crystallographer. As a consequence, we believe it is important to draw this altered interpretation of the crystal structures to the attention of readers. In both structures, the density for the backbone of GSH is clear and allows unequivocal assignment of the position of the tripeptide. In PDB coordinate set 3L9X, the density for the succinimido ring is very weak, making interpretation very speculative and the assignment rests on the identity of the ligand added to the crystallization mixture, for which there are two diastereomers in the solution—a possibility that provides some basis for weakening the density. However, in 3L9W there are two anomalies that affect the interpretation of the bound ligand. First, there is no density for the carbon atom attached to the sulfur of GSH and second, there is extra density adjacent to the position of sulfur that could be modelled as a constrained succinimido ring. However, this density could also be water or any other molecule that is trapped in the structure. Thus, while there is good evidence for the peptide, the evidence that it is in the GSH form is uncertain.
“There are no new data on either the structures or on the gating mechanism. However, we believe that we should be cautious in interpreting the structural data and that the field in general should be made aware of the alternative views of the electron density data. Note that the mutagenesis and spectroscopic data that were presented in the original manuscript are not affected by this alternative interpretation.”
Tarmo P. Roosild and Samantha Castronovo have decided not to sign this statement.
Ian R. Booth
Jess Healy
Samantha Miller
Christos Pliotas
Tim Rasmussen
Wendy Bartlett
Stuart J. Conway