Open AccessUse of thallium to identify monovalent cation binding sites in GroEL
Author(s) -
Kiser Philip D.,
Lorimer George H.,
Palczewski Krzysztof
Publication year - 2009
Publication title -
acta crystallographica section f
Language(s) - English
Resource type - Journals
ISSN - 1744-3091
DOI - 10.1107/s1744309109032928
Subject(s) - groel , groes , crystallography , binding site , cooperativity , chaperone (clinical) , chaperonin , chemistry , atp hydrolysis , cooperative binding , protein folding , biochemistry , atpase , enzyme , escherichia coli , medicine , pathology , gene
GroEL is a bacterial chaperone protein that assembles into a homotetradecameric complex exhibiting D 7 symmetry and utilizes the co‐chaperone protein GroES and ATP hydrolysis to assist in the proper folding of a variety of cytosolic proteins. GroEL utilizes two metal cofactors, Mg 2+ and K + , to bind and hydrolyze ATP. A K + ‐binding site has been proposed to be located next to the nucleotide‐binding site, but the available structural data do not firmly support this conclusion. Moreover, more than one functionally significant K + ‐binding site may exist within GroEL. Because K + has important and complex effects on GroEL activity and is involved in both positive (intra‐ring) and negative (inter‐ring) cooperativity for ATP hydrolysis, it is important to determine the exact location of these cation‐binding site(s) within GroEL. In this study, the K + mimetic Tl + was incorporated into GroEL crystals, a moderately redundant 3.94 Å resolution X‐ray diffraction data set was collected from a single crystal and the strong anomalous scattering signal from the thallium ion was used to identify monovalent cation‐binding sites. The results confirmed the previously proposed placement of K + next to the nucleotide‐binding site and also identified additional binding sites that may be important for GroEL function and cooperativity. These findings also demonstrate the general usefulness of Tl + for the identification of monovalent cation‐binding sites in protein crystal structures, even when the quality and resolution of the diffraction data are relatively low.