Spectral editing of intra- and inter-chain methyl-methyl NOEs in protein complexes

Visualizing the transiently populated closed-state of human HSP90 ATP binding domain

HSP90 are abundant molecular chaperones, assisting the folding of several hundred client proteins, including substrates involved in tumor growth or neurodegenerative diseases. A complex set of large ATP-driven structural changes occurs during HSP90 functional cycle. However, the existence of such structural rearrangements in apo HSP90 has remained unclear. Here, we identify a metastable excited state in the isolated human HSP90α ATP binding domain. We use solution NMR and mutagenesis to characterize structures of both ground and excited states. We demonstrate that in solution the HSP90α ATP binding domain transiently samples a functionally relevant ATP-lid closed state, distant by more than 30 Å from the ground state. NMR relaxation enables to derive information on the kinetics and thermodynamics of this interconversion, while molecular dynamics simulations establish that the ATP-lid in closed conformation is a metastable exited state. The precise description of the dynamics and structures sampled by human HSP90α ATP binding domain provides information for the future design of new therapeutic ligands.

NMR assignment of human HSP90 N-terminal domain bound to a long residence time resorcinol ligand

HSP90 is a major molecular chaperone that helps both folding and stabilization of various client proteins often implicated in growth control and cell survival such as kinases and transcription factors. However, among HSP90 clients are also found numerous oncoproteins and, through its assistance to them, HSP90 has consequently been reported as a promising anticancer target. Several ligand chemotypes, including resorcinol type ligands, were found to inhibit HSP90, most of them in an ATP competitive manner. Binding of some of these ligands modify significantly the NMR spectrum of the HSP90 ATP binding domain compared to the apo protein spectrum, hampering assignment transfer from the previously assigned human HSP90 apo state. Here we report the assignment of the ¹H_N, ¹⁵N, ¹³C', ¹³C_α, ¹³C_β, ¹H_methyl, and ¹³C_methyl chemical shifts of the 29 kDa HSP90 N-terminal domain bound to a long residence time resorcinol type inhibitor: 5-[4-(2-Fluoro-phenyl)-5-oxo-4,5-dihydro-1H-[1,2,4]triazol-3-yl]-N-furan-2-ylmethyl-2,4-dihydroxy-N-methyl-benzamide. 92% of the backbone resonances and 100% of the [¹H, ¹³C]-resonances of A^β, M^ε, T^γ, L^δ2, V^γ2 and I^δ1 methyl groups were successfully assigned, including for the first time the assignment of the segment covering the nucleotide/drug binding site. Secondary structure predictions based on the NMR assignment reveal a structural rearrangement of HSP90 N-terminal domain upon ligand binding. The long residence time ligand induces the formation of a continuous helix covering the ligand binding site of HSP90 N-terminal domain accounting for the large differences observed in the NMR spectra between the apo and bound proteins.

Backbone and methyl resonances assignment of the 87 kDa prefoldin from Pyrococcus horikoshii

Prefoldin is a heterohexameric protein assembly which acts as a co-chaperonin for the well conserved Hsp60 chaperonin, present in archaebacteria and the eukaryotic cell cytosol. Prefoldin is a holdase, capturing client proteins and subsequently transferring them to the Hsp60 chamber for refolding. The chaperonin family is implicated in the early stages of protein folding and plays an important role in proteostasis in the cytosol. Here, we report the assignment of 1HN, 15N, 13C', 13Cα, 13Cβ, 1Hmethyl, and 13Cmethyl chemical shifts of the 87 kDa prefoldin from the hyperthermophilic archaeon Pyrococcus horikoshii, consisting of two α and four β subunits. 100% of the [13C, 1H]-resonances of Aβ, Iδ1, Iδ2, Tγ2, Vγ2 methyl groups were successfully assigned for both subunits. For the β subunit, showing partial peak doubling, 80% of the backbone resonances were assigned. In the α subunit, large stretches of backbone resonances were not detectable due to slow (μs-ms) time scale dynamics. This conformational exchange limited the backbone sequential assignment of the α subunit to 57% of residues, which corresponds to 84% of visible NMR signals.

Optimized precursor to simplify assignment transfer between backbone resonances and stereospecifically labelled valine and leucine methyl groups: application to human Hsp90 N-terminal domain

Methyl moieties are highly valuable probes for quantitative NMR studies of large proteins. Hence, their assignment is of the utmost interest to obtain information on both interactions and dynamics of proteins in solution. Here, we present the synthesis of a new precursor that allows connection of leucine and valine pro-S methyl moieties to backbone atoms by linear ¹³C-chains. This optimized ²H/¹³C-labelled acetolactate precursor can be combined with existing ¹³C/²H-alanine and isoleucine precursors in order to directly transfer backbone assignment to the corresponding methyl groups. Using this simple approach leucine and valine pro-S methyl groups can be assigned using a single sample without requiring correction of ¹H/²H isotopic shifts on ¹³C resonances. The approach was demonstrated on the N-terminal domain of human HSP90, for which complete assignment of Ala-β, Ile-δ₁, Leu-δ₂, Met-ε, Thr-γ and Val-γ₂ methyl groups was obtained.