title: Direct NMR observation of a substrate protein bound to the chaperonin GroEL.
abstract: The reaction cycle and the major structural states of the molecular chaperone GroEL and its cochaperone, GroES, are well characterized. In contrast, very little is known about the nonnative states of the substrate polypeptide acted on by the chaperonin machinery. In this study, we investigated the substrate protein human dihydrofolate reductase (hDHFR) while bound to GroEL or to a single-ring analog, SR1, by NMR spectroscopy in solution under conditions where hDHFR was efficiently recovered as a folded, enzymatically active protein from the stable complexes upon addition of ATP and GroES. By using the NMR techniques of transverse relaxation-optimized spectroscopy (TROSY), cross-correlated relaxation-induced polarization transfer (CRIPT), and cross-correlated relaxation-enhanced polarization transfer (CRINEPT), bound hDHFR could be observed directly. Measurements of the buildup of hDHFR NMR signals by different magnetization transfer mechanisms were used to characterize the dynamic properties of the NMR-observable parts of the bound substrate. The NMR data suggest that the bound state includes random coil conformations devoid of stable native-like tertiary contacts and that the bound hDHFR might best be described as a dynamic ensemble of randomly structured conformers.
authors.affiliation: Institut für Molekularbiologie und Biophysik, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Horst
authors.forename: Eric B
authors.initials: EB
authors.lastname: Bertelsen
authors.forename: Jocelyne
authors.initials: J
authors.lastname: Fiaux
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wider
authors.forename: Arthur L
authors.initials: AL
authors.lastname: Horwich
authors.forename: Kurt
authors.initials: K
authors.lastname: Wüthrich
mesh_terms: D018835:Chaperonin 10 / Q000737:chemistry / Q000378:metabolism; D018834:Chaperonin 60 / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007930:Leucine / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D017510:Protein Folding; D013379:Substrate Specificity; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D018835:Chaperonin 10; D018834:Chaperonin 60; D013762:Tetrahydrofolate Dehydrogenase; D007930:Leucine