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Salmonella enterica serovar Typhimurium can induce both humoral and cell-mediated responses when establishing itself in the host. These responses are primarily stimulated against the lipopolysaccharide and major outer membrane (OM) proteins. OmpA is one of these major OM proteins. It comprises a N-terminal eight-stranded β-barrel transmembrane domain and a C-terminal domain (OmpA CTD ). The OmpA CTD and its homologs are believed to bind to peptidoglycan (PG) within the periplasm, maintaining bacterial osmotic homeostasis and modulating the permeability and integrity of the OM. Here we present the first crystal structures of the OmpA CTD from two pathogens: S. typhimurium (STOmpA CTD ) in open and closed forms and causative agent of Lyme Disease Borrelia burgdorferi (BbOmpA CTD ), in closed form. In the open form of STOmpA CTD , an aspartate residue from a long β2-α3 loop points into the binding pocket, suggesting that an anion group such as a carboxylate group from PG is favored at the binding site. In the closed form of STOmpA CTD and in the structure of BbOmpA CTD , a sulfate group from the crystallization buffer is tightly bound at the binding site. The differences between the closed and open forms of STOmpA CTD , suggest a large conformational change that includes an extension of α3 helix by ordering a part of β2-α3 loop. We propose that the sulfate anion observed in these structures mimics the carboxylate group of PG when bound to STOmpA CTD suggesting PG-anchoring mechanism. In addition, the binding of PG or a ligand mimic may enhance dimerization of STOmpA CTD , or possibly that of full length STOmpA., (© 2017 The Protein Society.)

We have developed an online NMR / X-ray Structure Pair Data Repository. The NIGMS Protein Structure Initiative (PSI) has provided many valuable reagents, 3D structures, and technologies for structural biology. The Northeast Structural Genomics Consortium was one of several PSI centers. NESG used both X-ray crystallography and NMR spectroscopy for protein structure determination. A key goal of the PSI was to provide experimental structures for at least one representative of each of hundreds of targeted protein domain families. In some cases, structures for identical (or nearly identical) constructs were determined by both NMR and X-ray crystallography. NMR spectroscopy and X-ray diffraction data for 41 of these "NMR / X-ray" structure pairs determined using conventional triple-resonance NMR methods with extensive sidechain resonance assignments have been organized in an online NMR / X-ray Structure Pair Data Repository. In addition, several NMR data sets for perdeuterated, methyl-protonated protein samples are included in this repository. As an example of the utility of this repository, these data were used to revisit questions about the precision and accuracy of protein NMR structures first outlined by Levy and coworkers several years ago (Andrec et al., Proteins 2007;69:449-465). These results demonstrate that the agreement between NMR and X-ray crystal structures is improved using modern methods of protein NMR spectroscopy. The NMR / X-ray Structure Pair Data Repository will provide a valuable resource for new computational NMR methods development., (© 2015 The Protein Society.)

YbbR domains are widespread throughout Eubacteria and are expressed as monomeric units, linked in tandem repeats or cotranslated with other domains. Although the precise role of these domains remains undefined, the location of the multiple YbbR domain-encoding ybbR gene in the Bacillus subtilis glmM operon and its previous identification as a substrate for a surfactin-type phosphopantetheinyl transferase suggests a role in cell growth, division, and virulence. To further characterize the YbbR domains, structures of two of the four domains (I and IV) from the YbbR-like protein of Desulfitobacterium hafniense Y51 were solved by solution nuclear magnetic resonance and X-ray crystallography. The structures show the domains to have nearly identical topologies despite a low amino acid identity (23%). The topology is dominated by β-strands, roughly following a "figure 8" pattern with some strands coiling around the domain perimeter and others crossing the center. A similar topology is found in the C-terminal domain of two stress-responsive bacterial ribosomal proteins, TL5 and L25. Based on these models, a structurally guided amino acid alignment identifies features of the YbbR domains that are not evident from naïve amino acid sequence alignments. A structurally conserved cis-proline (cis-Pro) residue was identified in both domains, though the local structure in the immediate vicinities surrounding this residue differed between the two models. The conservation and location of this cis-Pro, plus anchoring Val residues, suggest this motif may be significant to protein function., (Copyright © 2011 The Protein Society.)

Pseudomonas aeruginosa is the prototypical biofilm-forming gram-negative opportunistic human pathogen. P. aeruginosa is causatively associated with nosocomial infections and with cystic fibrosis. Antibiotic resistance in some strains adds to the inherent difficulties that result from biofilm formation when treating P. aeruginosa infections. Transcriptional profiling studies suggest widespread changes in the proteome during quorum sensing and biofilm development. Many of the proteins found to be upregulated during these processes are poorly characterized from a functional standpoint. Here, we report the solution NMR structure of PA1324, a protein of unknown function identified in these studies, and provide a putative biological functional assignment based on the observed prealbumin-like fold and FAST-NMR ligand screening studies. PA1324 is postulated to be involved in the binding and transport of sugars or polysaccharides associated with the peptidoglycan matrix during biofilm formation.

The ribosomal protein S17E from the archaeon Methanobacterium thermoautotrophicum is a component of the 30S ribosomal subunit. S17E is a 62-residue protein conserved in archaea and eukaryotes and has no counterparts in bacteria. Mammalian S17E is a phosphoprotein component of eukaryotic ribosomes. Archaeal S17E proteins range from 59 to 79 amino acids, and are about half the length of the eukaryotic homologs which have an additional C-terminal region. Here we report the three-dimensional solution structure of S17E. S17E folds into a small three-helix bundle strikingly similar to the FF domain of human HYPA/FBP11, a novel phosphopeptide-binding fold. S17E bears a conserved positively charged surface acting as a robust scaffold for molecular recognition. The structure of M. thermoautotrophicum S17E provides a template for homology modeling of eukaryotic S17E proteins in the family.

The solution structure of protein AF2095 from the thermophilic archaea Archaeglobus fulgidis, a 123-residue (13.6-kDa) protein, has been determined by NMR methods. The structure of AF2095 is comprised of four alpha-helices and a mixed beta-sheet consisting of four parallel and anti-parallel beta-strands, where the alpha-helices sandwich the beta-sheet. Sequence and structural comparison of AF2095 with proteins from Homo sapiens, Methanocaldococcus jannaschii, and Sulfolobus solfataricus reveals that AF2095 is a peptidyl-tRNA hydrolase (Pth2). This structural comparison also identifies putative catalytic residues and a tRNA interaction region for AF2095. The structure of AF2095 is also similar to the structure of protein TA0108 from archaea Thermoplasma acidophilum, which is deposited in the Protein Data Bank but not functionally annotated. The NMR structure of AF2095 has been further leveraged to obtain good-quality structural models for 55 other proteins. Although earlier studies have proposed that the Pth2 protein family is restricted to archeal and eukaryotic organisms, the similarity of the AF2095 structure to human Pth2, the conservation of key active-site residues, and the good quality of the resulting homology models demonstrate a large family of homologous Pth2 proteins that are conserved in eukaryotic, archaeal, and bacterial organisms, providing novel insights in the evolution of the Pth and Pth2 enzyme families.

We report NMR assignments and solution structure of the 71-residue 30S ribosomal protein S28E from the archaean Pyrococcus horikoshii, target JR19 of the Northeast Structural Genomics Consortium. The structure, determined rapidly with the aid of automated backbone resonance assignment (AutoAssign) and automated structure determination (AutoStructure) software, is characterized by a four-stranded beta-sheet with a classic Greek-key topology and an oligonucleotide/oligosaccharide beta-barrel (OB) fold. The electrostatic surface of S28E exhibits positive and negative patches on opposite sides, the former constituting a putative binding site for RNA. The 13 C-terminal residues of the protein contain a consensus sequence motif constituting the signature of the S28E protein family. Surprisingly, this C-terminal segment is unstructured in solution.

The ribosomal protein S28E from the archaeon Methanobacterium thermoautotrophicum is a component of the 30S ribosomal subunit. Sequence homologs of S28E are found only in archaea and eukaryotes. Here we report the three-dimensional solution structure of S28E by NMR spectroscopy. S28E contains a globular region and a long C-terminal tail protruding from the core. The globular region consists of four antiparallel beta-strands that are arranged in a Greek-key topology. Unique features of S28E include an extended loop L2-3 that folds back onto the protein and a 12-residue charged C-terminal tail with no regular secondary structure and greater flexibility relative to the rest of the protein. The structural and surface resemblance to OB-fold family of proteins and the presence of highly conserved basic residues suggest that S28E may bind to RNA. A broad positively charged surface extending over one side of the beta-barrel and into the flexible C terminus may present a putative binding site for RNA.

The structure of Vibrio cholerae protein VC0424 was determined by NMR spectroscopy. VC0424 belongs to a conserved family of bacterial proteins of unknown function (COG 3076). The structure has an alpha-beta sandwich architecture consisting of two layers: a four-stranded antiparallel beta-sheet and three side-by-side alpha-helices. The secondary structure elements have the order alphabetaalphabetabetaalphabeta along the sequence. This fold is the same as the ferredoxin-like fold, except with an additional long N-terminal helix, making it a variation on this common motif. A cluster of conserved surface residues on the beta-sheet side of the protein forms a pocket that may be important for the biological function of this conserved family of proteins.

As part of the Northeast Structural Genomics Consortium pilot project focused on small eukaryotic proteins and protein domains, we have determined the NMR structure of the protein encoded by ORF YML108W from Saccharomyces cerevisiae. YML108W belongs to one of the numerous structural proteomics targets whose biological function is unknown. Moreover, this protein does not have sequence similarity to any other protein. The NMR structure of YML108W consists of a four-stranded beta-sheet with strand order 2143 and two alpha-helices, with an overall topology of betabetaalphabetabetaalpha. Strand beta1 runs parallel to beta4, and beta2:beta1 and beta4:beta3 pairs are arranged in an antiparallel fashion. Although this fold belongs to the split betaalphabeta family, it appears to be unique among this family; it is a novel arrangement of secondary structure, thereby expanding the universe of protein folds.