Structural and functional analysis of Hsp90

Hsp90 is a ubiquitous molecular chaperone whose fundamental cellular role is unknown. However, Hsp90 is known to play a critical role in the regulation of a broad array of proteins involved in intracellular signaling including nuclear steroid receptors such as the estrogen and glucocorticoid receptors; other ligand-gated transcription factors such as the aryl hydrocarbon class of PAS domain receptors; numerous serine/threonine and tyrosine kinases; and nitric oxide synthase. As a first step in understanding the mechanism of Hsp90 function, we have nearly completed the determination of the structure of the full length E. coli Hsp90: htpg. The next steps will be to examine the structural effects of nucleotide hydrolysis, make complexes with peptides from target protein ligands, and to make complexes with the estrogen receptor LBD and/or with other co-chaperone proteins.

Relevant Publications

Shiau AK, Harris SF, Southworth DR, Agard DA, "Structural Analysis of E. coli hsp90 Reveals Dramatic Nucleotide-Dependent Conformational Rearrangements," Cell. 2006 Oct 20;127(2):329-340(html or pdf).

Seth F. Harris, Andrew K. Shiau and David A. Agard, "The Crystal Structure of the Carboxy-Terminal Dimerization Domain of htpG, the Escherichia coli Hsp90, Reveals a Potential Substrate Binding Site," Structure, (2004) 12(6):1087-1097 (pdf).

Overall Structure of Apo Full-Length HtpG

(A and B) Two orthogonal ribbon views of the apo full-length dimer. The amino-terminal domain (NTD) (blue) contains the ‘‘active-site lid’’ region (helices H4 and H5; dark blue cylinders). The middle domain (MD) (green) contains the extended ‘‘src loop’’ (dark green tube), and the carboxy-terminal domain (CTD) is shown in gold. The exposed carboxy terminal helices (H21 and H21’) (red boxes) are disordered in this structure and are illustrated based on alignment with the isolated CTD structure.
(C and D) Two orthogonal surface views indicating functional regions of the apo full-length dimer. The NTD lid (blue), MD src loop (green), and CTD amphipathic helices (red and modeled as in A) present hydrophobic surfaces into the larger intra-dimer cleft proposed to be important for client-protein binding. Additionally, the surface is colored (purple charged loop) to show the predicted location of the highly charged sequence present in eukaryotic hsp90 but absent in HtpG. The MD loop and helix H10 that contain residues potentially important for ATP hydrolysis (yellow) are also shown.