Joel Berendzen

Automated MAD and MIR structure solution.

A fully automated procedure for solving MIR and MAD structures has been developed using a scoring scheme to convert the structure-solution process into an optimization problem.

Crystal structures of myoglobin-ligand complexes at near-atomic resolution.

We have used x-ray crystallography to determine the structures of sperm whale myoglobin (Mb) in four different ligation states (unligated, ferric aquomet, oxygenated, and carbonmonoxygenated) to a resolution of better than 1.2 A. Data collection and analysis were performed in as much the same way as possible to reduce model bias in differences between structures. The structural differences among the ligation states are much smaller than previously estimated, with differences of <0.25 A root-mean-square deviation among all atoms. One structural parameter previously thought to vary among the ligation states, the proximal histidine (His-93) azimuthal angle, is nearly identical in all the ferrous complexes, although the tilt of the proximal histidine is different in the unligated form. There are significant differences, however, in the heme geometry, in the position of the heme in the pocket, and in the distal histidine (His-64) conformations. In the CO complex the majority conformation of ligand is at an angle of 18 +/- 3 degrees with respect to the heme plane, with a geometry similar to that seen in encumbered model compounds; this angle is significantly smaller than reported previously by crystallographic studies on monoclinic Mb crystals, but still significantly larger than observed by photoselection. The distal histidine in unligated Mb and in the dioxygenated complex is best described as having two conformations. Two similar conformations are observed in MbCO, in addition to another conformation that has been seen previously in low-pH structures where His-64 is doubly protonated. We suggest that these conformations of the distal histidine correspond to the different conformational substates of MbCO and MbO(2) seen in vibrational spectra. Full-matrix refinement provides uncertainty estimates of important structural parameters. Anisotropic refinement yields information about correlated disorder of atoms; we find that the proximal (F) helix and heme move approximately as rigid bodies, but that the distal (E) helix does not.

Structural alterations for proton translocation in the M state of wild-type bacteriorhodopsin

The transport of protons across membranes is an important process in cellular bioenergetics. The light-driven proton pump bacteriorhodopsin is the best-characterized protein providing this function. Photon energy is absorbed by the chromophore retinal, covalently bound to Lys 216 via a protonated Schiff base. The light-induced all-trans to 13-cis isomerization of the retinal results in deprotonation of the Schiff base followed by alterations in protonatable groups within bacteriorhodopsin. The changed force field induces changes, even in the tertiary structure, which are necessary for proton pumping. The recent report of a high-resolution X-ray crystal structure for the late M intermediate of a mutant bacteriorhopsin (with Asp 96→Asn) displays the structure of a proton pathway highly disturbed by the mutation. To observe an unperturbed proton pathway, we determined the structure of the late M intermediate of wild-type bacteriorhodopsin (2.25 Å resolution). The cytoplasmic side of our M2 structure shows a water net that allows proton transfer from the proton donor group Asp 96 towards the Schiff base. An enlarged cavity system above Asp 96 is observed, which facilitates the de- and reprotonation of this group by fluctuating water molecules in the last part of the cycle.

Engineering soluble proteins for structural genomics

Structural genomics has the ambitious goal of delivering three-dimensional structural information on a genome-wide scale. Yet only a small fraction of natural proteins are suitable for structure determination because of bottlenecks such as poor expression, aggregation, and misfolding of proteins, and difficulties in solubilization and crystallization. We propose to overcome these bottlenecks by producing soluble, highly expressed proteins that are derived from and closely related to their natural homologs. Here we demonstrate the utility of this approach by using a green fluorescent protein (GFP) folding reporter assay to evolve an enzymatically active, soluble variant of a hyperthermophilic protein that is normally insoluble when expressed in Escherichia coli, and determining its structure by X-ray crystallography. Analysis of the structure provides insight into the substrate specificity of the enzyme and the improved solubility of the variant.

Crystal structure and functional analysis of the SurE protein identify a novel phosphatase family

Homologs of the Escherichia coli surE gene are present in many eubacteria and archaea. Despite the evolutionary conservation, little information is available on the structure and function of their gene products. We have determined the crystal structure of the SurE protein from Thermotoga maritima. The structure reveals the dimeric arrangement of the subunits and an active site around a bound metal ion. We also demonstrate that the SurE protein exhibits a divalent metal ion-dependent phosphatase activity that is inhibited by vanadate or tungstate. In the vanadate- and tungstate-complexed structures, the inhibitors bind adjacent to the divalent metal ion. Our structural and functional analyses identify the SurE proteins as a novel family of metal ion-dependent phosphatases.

Structure of translation initiation factor 5A from Pyrobaculum aerophilum at 1.75 å resolution

BACKGROUND Translation initiation factor 5A (IF-5A) is reported to be involved in the first step of peptide bond formation in translation, to be involved in cell-cycle regulation and to be a cofactor for the Rev and Rex transactivator proteins of human immunodeficiency virus-1 and T-cell leukemia virus I, respectively. IF-5A contains an unusual amino acid, hypusine (N-epsilon-(4-aminobutyl-2-hydroxy)lysine), that is required for its function. The first step in the post-translational modification of lysine to hypusine is catalyzed by the enzyme deoxyhypusine synthase, the structure of which has been published recently. RESULTS IF-5A from the archebacterium Pyrobaculum aerophilum has been heterologously expressed in Escherichia coli with selenomethionine substitution. The crystal structure of IF-5A has been determined by multiwavelength anomalous diffraction and refined to 1.75 A. Unmodified P. aerophilum IF-5A is found to be a beta structure with two domains and three separate hydrophobic cores. CONCLUSIONS The lysine (Lys42) that is post-translationally modified by deoxyhypusine synthase is found at one end of the IF-5A molecule in an turn between beta strands beta4 and beta5; this lysine residue is freely solvent accessible. The C-terminal domain is found to be homologous to the cold-shock protein CspA of E. coli, which has a well characterized RNA-binding fold, suggesting that IF-5A is involved in RNA binding.

The TB structural genomics consortium: a resource for Mycobacterium tuberculosis biology

The TB Structural Genomics Consortium is an organization devoted to encouraging, coordinating, and facilitating the determination and analysis of structures of proteins from Mycobacterium tuberculosis. The Consortium members hope to work together with other M. tuberculosis researchers to identify M. tuberculosis proteins for which structural information could provide important biological information, to analyze and interpret structures of M. tuberculosis proteins, and to work collaboratively to test ideas about M. tuberculosis protein function that are suggested by structure or related to structural information. This review describes the TB Structural Genomics Consortium and some of the proteins for which the Consortium is in the progress of determining three-dimensional structures.

The TB structural genomics consortium: Providing a structural foundation for drug discovery

Structural genomics, the large-scale determination of protein structures, promises to provide a broad structural foundation for drug discovery. The tuberculosis (TB) Structural Genomics Consortium is devoted to encouraging, coordinating, and facilitating the determination of structures of proteins from Mycobacterium tuberculosis and hopes to determine 400 TB protein structures over 5 years. The Consortium has determined structures of 28 proteins from TB to date. These protein structures are already providing a basis for drug discovery efforts.

Evaluation of macromolecular electron-density map quality using the correlation of local r.m.s. density

The correlation of local r.m.s. density is shown to be a good measure of the presence of distinct solvent and macromolecule regions in macromolecular electron-density maps.

Bayesian Correlated MAD Phasing

A Bayesian treatment for phase calculation in the multiwavelength anomalous diffraction (MAD) technique is presented. This approach explicitly treats effects of errors correlated among measurements at different wavelengths and between Bijvoet pairs. The resulting method, which is called Bayesian correlated MAD phasing, gives proper statistical consideration to all data and does not give special treatment to data from a particular wavelength. Results obtained using Bayesian correlated MAD phasing and two other strategies on both a model test case and on data obtained in two actual MAD experiments are compared. Although all procedures performed well when the completeness of the data was high, it is shown that Bayesian correlated MAD phasing is more robust with respect to incompleteness of data than the other methods are. At 60% completeness the improvement over other methods for the examples given was nearly 50% in the correlation coefficients, and made a substantial difference in the interpretability of an electron-density map.