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Laboratories often repeatedly determine the structure of a given protein under a variety of conditions, mutations, modifications, or in a number of states. This approach can be cumbersome and tedious. Given then a database of structures, identifiers, and corresponding (1)H,(15)N-HSQC NMR spectra for homologous proteins, we investigated whether structural information could be ascertained for a new homolog solely from its (1)H,(15)N-HSQC NMR spectrum. We addressed this question with two different approaches. First, we used a semi-automated approach with the program, ORBplus. ORBplus looks for patterns in the chemical shifts and correlates these commonalities to the explicit property of interest. ORBplus ranks resonances based on consistency of the magnitude and direction of the chemical shifts within the database, and the chemical shift correlation of the unknown protein with the database. ORBplus visualizes the results by a histogram and a vector diagram, and provides residue specific predictions on structural similarities with the database. The second method we used was partial least squares (PLS), which is a multivariate statistical technique used to correlate response and predictor variables. We investigated the ability of these methods to predict the tertiary structure of the contractile regulatory protein troponin C. Troponin C undergoes a closed-to-open conformational change, which is coupled to its function in muscle. We found that both ORBplus and PLS were able to identify patterns in the (1)H,(15)N-HSQC NMR data from different states of troponin C that correlated to its conformation.

We have addressed the electrostatic interactions occurring between the inhibitory region of cardiac troponin I with the C-lobe of troponin C using scanning glycine mutagenesis of the inhibitory region. We report variations in the electric potentials due to mutation of charged residues within this complex based upon the solved NMR structure (1OZS). These results demonstrate the importance of electrostatics within this complex, and it is proposed that electrostatic interactions are integral to the formation and function of larger ternary troponin complexes. To address this hypothesis, we report (15)N NMR relaxation measurements, which suggest that, within a ternary complex involving the C-lobe and the N-terminal region of troponin I (residues 34-71), the inhibitory region maintains the electrostatic interactions with the E-helix of the C-lobe as observed within the binary complex. These results imply that, in solution, the cardiac troponin complex behaves in a manner consistent with that of the crystal structure of the skeletal isoform (1YTZ). A cardiac troponin complex possessing domain orientations similar to that of the skeletal isoform provides structural insights into altered troponin I activities as observed for the familial hypertrophic cardiomyopathy mutation R144G and phosphorylation of Thr142.

Complete and accurate NMR spectral assignment is a prerequisite for high-throughput automated structure determination of biological macromolecules. However, completely automated assignment procedures generally encounter difficulties for all but the most ideal data sets. Sources of these problems include difficulty in resolving correlations in crowded spectral regions, as well as complications arising from dynamics, such as weak or missing peaks, or atoms exhibiting more than one peak due to exchange phenomena. Smartnotebook is a semi-automated assignment software package designed to combine the best features of the automated and manual approaches. The software finds and displays potential connections between residues, while the spectroscopist makes decisions on which connection is correct, allowing rapid and robust assignment. In addition, smartnotebook helps the user fit chains of connected residues to the primary sequence of the protein by comparing the experimentally determined chemical shifts with expected shifts derived from a chemical shift database, while providing bookkeeping throughout the assignment procedure.

VADAR (Volume Area Dihedral Angle Reporter) is a comprehensive web server for quantitative protein structure evaluation. It accepts Protein Data Bank (PDB) formatted files or PDB accession numbers as input and calculates, identifies, graphs, reports and/or evaluates a large number (>30) of key structural parameters both for individual residues and for the entire protein. These include excluded volume, accessible surface area, backbone and side chain dihedral angles, secondary structure, hydrogen bonding partners, hydrogen bond energies, steric quality, solvation free energy as well as local and overall fold quality. These derived parameters can be used to rapidly identify both general and residue-specific problems within newly determined protein structures. The VADAR web server is freely accessible at http://redpoll.pharmacy.ualberta.ca/vadar.

A suite of programs called CAMRA (Computer Aided Magnetic Resonance Assignment) has been developed for computer assisted residue-specific assignments of proteins. CAMRA consists of three units: ORB, CAPTURE and PROCESS. ORB predicts NMR chemical shifts for unassigned proteins using a chemical shift database of previously assigned homologous proteins supplemented by a statistically derived chemical shift database in which the shifts are categorized according to their residue, atom and secondary structure type. CAPTURE generates a list of valid peaks from NMR spectra by filtering out noise peaks and other artifacts and then separating the derived peak list into distinct spin systems. PROCESS combines the chemical shift predictions from ORB with the spin systems identified by CAPTURE to obtain residue specific assignments. PROCESS ranks the top choices for an assignment along with scores and confidence values. In contrast to other auto-assignment programs, CAMRA does not use any connectivity information but instead is based solely on matching predicted shifts with observed spin systems. As such, CAMRA represents a new and unique approach for the assignment of protein NMR spectra. CAMRA will be particularly useful in conjunction with other assignment methods and under special circumstances, such as the assignment of flexible regions in proteins where sufficient NOE information is generally not available. CAMRA was tested on two medium-sized proteins belonging to the chemokine family. It was found to be effective in predicting the assignment providing a database of previously assigned proteins with at least 30% sequence identity is available. CAMRA is versatile and can be used to include and evaluate heteronuclear and three-dimensional experiments.

A computer program has been developed to accurately and automatically predict the 1H and 13C chemical shifts of unassigned proteins on the basis of sequence homology. The program (called SHIFTY) uses standard sequence alignment techniques to compare the sequence of an unassigned protein against the BioMagResBank--a public database containing sequences and NMR chemical shifts of nearly 200 assigned proteins [Seavey et al. (1991) J Biomol. NMR, 1, 217-236]. From this initial sequence alignment, the program uses a simple set of rules to directly assign or transfer a complete set of 1H or 13C chemical shifts (from the previously assigned homologues) to the unassigned protein. This 'homologous assignment' protocol takes advantage of the simple fact that homologous proteins tend to share both structural similarity and chemical shift similarity. SHIFTY has been extensively tested on more than 25 medium-sized proteins. Under favorable circumstances, this program can predict the 1H or 13C chemical shifts of proteins with an accuracy far exceeding any other method published to date. With the exponential growth in the number of assigned proteins appearing in the literature (now at a rate of more than 150 per year), we believe that SHIFTY may have widespread utility in assigning individual members in families of related proteins, an endeavor that accounts for a growing portion of the protein NMR work being done today.

SEQSEE (SEQuence SEEker) is a multi-purpose, menu-driven suite of programs designed to provide a fully integrated, state-of-the-art package for the analysis and display of protein sequences and protein databases. It is currently configured to run on most UNIX-based machines including Sun, SGI and NeXT workstations with conversion to other architectures (e.g. Vax or Cray) being a relatively simple task. SEQSEE is capable of performing nearly all of the analytical and comparative tasks found in most comprehensive commercially available software packages. These include sequence/database searching, sequence retrieval, sequence entry and editing, statistical sequence analysis, multiple sequence alignment, flexible pattern matching, and secondary structure prediction. SEQSEE also integrates a number of unique databases which allow it to perform many additional functions such as structure-based sequence alignments and homology-based secondary structure prediction. Additional enhancements to many previously published algorithms have substantially improved the performance of SEQSEE over that found for most other commercial products. The source code, the documentation and all of the required databases for SEQSEE are freely available and may be obtained by anonymous ftp.