0225180a_Gruner

1. Ion Transporters: CHESS Pressure-Freezing Helps See Important Details R. A. Albright, J.-L. V. Ibar, C. U. Kim, S. M. Gruner and J. H. Morais-Cabral (Yale University) DMR-0225180 KtrA is the regulatory domain of KtrB, a K+ transporter which is important in controlling the potassium concentration in cells. There has been disagreement about how KtrA molecules are arranged in functional complexes. Crystal structures by Morais-Cabral and co-workers reveal that KtrA forms various octameric ring forms, ranging from "squares" to "rectangles". A bound NADH ligand was clearly seen only when crystals were pressure-frozen using a method developed at CHESS. A new model for KtrAB has been developed that provides insight into how this important transporter works. The work was recently published in Cell (2006), Vol. 126, 1147-1159 Different conformations of the KtrA octameric ring are found in crystals grown under slightly different conditions. Each ring is composed of four pairs of KtrA molecules; one member of each pair is colored red and one is blue. Bound ligands (small signaling molecules) are shown in green and the yellow dots are markers to help follow how KtrA molecules move as the ring changes shape.