Protein NMR chemical shifts are highly sensitive to local structure. A robust protocol is described that exploits this relation for de novo protein structure generation, using as input experimental parameters the 13 C ␣ , 13 C ␤ , 13 C , 15 N, 1 H ␣ and 1 H N NMR chemical shifts. These shifts are generally available at the early stage of the traditional NMR structure determination process, before the collection and analysis of structural restraints. The chemical shift based structure determination protocol uses an empirically optimized procedure to select protein fragments from the Protein Data Bank, in conjunction with the standard ROSETTA Monte Carlo assembly and relaxation methods. Evaluation of 16 proteins, varying in size from 56 to 129 residues, yielded full-atom models that have 0.7-1.8 Å root mean square deviations for the backbone atoms relative to the experimentally determined x-ray or NMR structures. The strategy also has been successfully applied in a blind manner to nine protein targets with molecular masses up to 15.4 kDa, whose conventional NMR structure determination was conducted in parallel by the Northeast Structural Genomics Consortium. This protocol potentially provides a new direction for high-throughput NMR structure determination. molecular fragment replacement ͉ protein structure prediction ͉ ROSETTA ͉ structural genomics

Molecular chaperones prevent aggregation and misfolding of proteins but scarcity of structural data has impeded an understanding of the recognition and anti-aggregation mechanisms. Here we report the solution structure, dynamics and energetics of three Trigger Factor (TF) chaperone molecules in complex with alkaline phosphatase (PhoA) captured in the unfolded state. Our data show that TF uses multiple sites to bind to several regions of the PhoA substrate protein primarily through hydrophobic contacts. NMR relaxation experiments show that TF interacts with PhoA in a highly dynamic fashion but as the number and length of the PhoA regions engaged by TF increases, a more stable complex gradually emerges. Multivalent binding keeps the substrate protein in an extended, unfolded conformation. The results show how molecular chaperones recognize unfolded polypeptides and how by acting as unfoldases and holdases prevent the aggregation and premature (mis)folding of unfolded proteins.

Conventional protein structure determination from nuclear magnetic resonance data relies heavily on side-chain proton-proton distances. The necessary side-chain resonance assignment, however, is labor intensive and prone to error. Here we show that structures can be accurately determined without NMR information on the sidechains for proteins up to 25 kDa by incorporating backbone chemical shifts, residual dipolar couplings, and amide proton distances into the Rosetta protein structure modelling methodology. These data, which are too sparse for conventional methods, serve only to guide conformational search towards the lowest energy conformations in the folding landscape; the details of the computed models are determined by the physical chemistry implicit in the Rosetta all atom energy function. The new method is not hindered by the deuteration required to suppress nuclear relaxation processes for proteins greater than 15 kDa, and should enable routine NMR structure determination for larger proteins.The first step in protein structure determination by NMR is chemical shift assignment for the backbone atoms. In contrast to the subsequent assignment of the sidechains, this is now rapid, reliable, and largely automated (1-5). Global backbone structural information complementing the local structure information provided by backbone chemical shift assignments (6,7), can be obtained from H N -H N NOESY, residual dipolar coupling (RDC) (8), and other (9,10) experiments. For larger proteins, deuteration becomes necessary to circumvent the efficient spin relaxation properties resulting from their higher rotational correlation times (11,12), but removing protons also eliminates long range NOESY information from sidechains except for selectively protonated sidechain moieties (13). The difficulty in determining accurate structures with no or limited sidechain information is a # To whom correspondence should be addressed. Phone: (206) 543-1295, Fax: (206) Here we show that structures of proteins up to 200 residues (23 kDa) can be determined using information from backbone (H N , N, C α , C β , C') NMR data by taking advantage of the conformational sampling and all atom energy function in the Rosetta structure prediction methodology, which for small proteins in favorable cases can produce atomic accuracy models starting from sequence information alone(15). Structure prediction in Rosetta proceeds in two steps; first a low resolution exploration phase using Monte-Carlo fragment assembly and a coarse-grained energy function, and second a computationally expensive refinement phase which cycles between combinatorial sidechain optimization and gradientbased minimization of all torsional degrees of freedom in a physically-realistic all-atom forcefield(15). The primary obstacle to Rosetta structure prediction from amino acid sequence information alone is conformational sampling; native structures almost always have lower energies than non-native conformations, but are very seldom sampled in unbiased trajectories. Incorpora...

We have developed an approach for determining NMR structures of proteins over 20 kDa that utilizes sparse distance restraints obtained using transverse relaxation optimized spectroscopy experiments on perdeuterated samples to guide RASREC Rosetta NMR structure calculations. The method was tested on 11 proteins ranging from 15 to 40 kDa, seven of which were previously unsolved. The RASREC Rosetta models were in good agreement with models obtained using traditional NMR methods with larger restraint sets. In five cases X-ray structures were determined or were available, allowing comparison of the accuracy of the Rosetta models and conventional NMR models. In all five cases, the Rosetta models were more similar to the X-ray structures over both the backbone and side-chain conformations than the "best effort" structures determined by conventional methods. The incorporation of sparse distance restraints into RASREC Rosetta allows routine determination of high-quality solution NMR structures for proteins up to 40 kDa, and should be broadly useful in structural biology.nuclear magnetic resonance | sparse data | maltose binding protein | structural genomics | genetic algorithms A dvances in hardware, sample preparation, pulse sequence development, and refinement techniques have expanded the size and complexity of proteins accessible to structure determination by solution-state NMR to include proteins that, until recently, were exclusively the realm of X-ray crystallography (1-3). However, despite a number of landmark studies (4-7), only a small percentage of structures solved by NMR and deposited in the Protein Data Bank exceed 20 kDa in molecular weight. Larger structures need to be assembled by combining structural information from individual domains, and require additional techniques to elucidate the spatial arrangement, such as shape fitting (5) and/or paramagnetic restraints (8).The 20-kDa general limit coincides with the two fundamental problems in solution-state NMR: resonance overlap and progressive increase in the transverse relaxation rate (1∕T 2 ). As the size of a molecule increases, so does the rotational correlation time and, consequently, the efficiency of 1 H-1 H relaxation mechanisms. One way to suppress these effects is to incorporate deuterium into the protein sample, diluting the 1 H-1 H relaxation networks and increasing 13 C and 15 N relaxation times, resulting in sharper line widths and dramatic improvement of the signalto-noise ratios (2, 9, 10). Perdeuteration is generally required for studies of larger proteins (11-14), particularly membrane proteins (15, 16).Unfortunately, deuteration also eliminates the majority of 1 H-1 H NOEs, the main source of long-range distance information in solution-state NMR. Several methods have emerged for reintroducing protons at selected sites to function as distance probes in the structure (11,17). Methyl groups of isoleucine δ1, leucine, and valine side chains are straightforward to label with 13 C and 1 H isotopes in an otherwise deuterated protein sample (12, ...