adenosine-5--(n-ethylcarboxamide) and 2-chloro-2--3--dideoxyadenosine

GRP94, the endoplasmic reticulum (ER) paralog of the chaperone Hsp90, plays an essential role in the structural maturation or secretion of a subset of proteins destined for transport to the cell surface, such as the Toll-like receptors 2 and 4, and IgG, respectively. GRP94 differs from cytoplasmic Hsp90 by exhibiting very weak ATP binding and hydrolysis activity. GRP94 also binds selectively to a series of substituted adenosine analogs. The high resolution crystal structures at 1.75-2.1 A of the N-terminal and adjacent charged domains of GRP94 in complex with N-ethylcarboxamidoadenosine, radicicol, and 2-chlorodideoxyadenosine reveals a structural mechanism for ligand discrimination among hsp90 family members. The structures also identify a putative subdomain that may act as a ligand-responsive switch. The residues of the charged region fold into a disordered loop whose termini are ordered and continue the twisted beta sheet that forms the structural core of the N-domain. This continuation of the beta sheet past the charged domain suggests a structural basis for the association of the N-terminal and middle domains of the full-length chaperone.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Amino Acid Sequence; Animals; Crystallography, X-Ray; Cytoplasm; Dideoxyadenosine; Dimerization; Dogs; Electrons; Endoplasmic Reticulum; Glutathione Transferase; HSP70 Heat-Shock Proteins; HSP90 Heat-Shock Proteins; Lactones; Ligands; Macrolides; Membrane Proteins; Models, Chemical; Models, Molecular; Molecular Sequence Data; Protein Binding; Protein Conformation; Protein Structure, Tertiary; Recombinant Fusion Proteins; Sequence Homology, Amino Acid; Substrate Specificity