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Biomedical subjects

Brian V Geisbrecht

Publications and source records attributed to Brian V Geisbrecht.

13 recordsLinked to original sources
PubMed2006

The solution structure of antigen MPT64 from Mycobacterium tuberculosis defines a new family of beta-grasp proteins.

The MPT64 protein and its homologs form a highly conserved family of secreted proteins with unknown function that are found within the pathogenic Mycobacteria genus. The founding member of this family from Mycobacterium tuberculosis (MPT64 or protein Rv1980c) is expressed only when Mycobacteria cells are actively dividing. By virtue of this relatively unique expression profile, Rv1980c is currently under phase III clinical trials to evaluate its potential to replace tuberculin, or purified protein derivative, as the rapid diagnostic of choice for detection of active tuberculosis infection. We describe here the NMR solution structure of Rv1980c. This structure reveals a previously undescribed fold that is based upon a variation of a beta-grasp motif most commonly found in protein-protein interaction domains. Examination of this structure in conjunction with multiple sequence alignments of MPT64 homologs identifies a candidate ligand-binding site, which may help guide future studies of Rv1980c function. The work presented here also suggests structure-based approaches for increasing the antigenic potency of a Rv1980c-based diagnostic.

Amino Acid Motifs↗
PubMed2006

Structure of a heparin-dependent complex of Hedgehog and Ihog.

Hedgehog (Hh) signaling molecules mediate key tissue-patterning events during animal development, and inappropriate activation of Hh signaling in adults has been associated with human cancers. Recently, a conserved family of type I integral membrane proteins required for normal response to the Hh signal was discovered. One member of this family, Ihog (interference hedgehog), functions upstream or at the level of Patched (Ptc), but how Ihog participates in Hh signaling remains unclear. Here, we show that heparin binding induces Ihog dimerization and is required to mediate high-affinity interactions between Ihog and Hh. We also present crystal structures of a Hh-binding fragment of Ihog, both alone and complexed with Hh. Heparin is not well ordered in these structures, but a basic cleft in the first FNIII domain of Ihog (IhogFn1) is shown by mutagenesis to mediate heparin binding. These results establish that Hh directly binds Ihog and provide the first demonstration of a specific role for heparin in Hh responsiveness.

Animals↗
PubMed2006

Suppression of experimental autoimmune encephalomyelitis by extracellular adherence protein of Staphylococcus aureus.

Multiple sclerosis (MS) is a devastating inflammatory disorder of the central nervous system (CNS). A major hallmark of MS is the infiltration of T cells reactive against myelin components. T cell infiltration is mediated by the interaction of integrins of the beta1 and beta2 family expressed by lymphocytes with their endothelial counter-receptors, vascular cell adhesion molecule 1 and intercellular adhesion molecule (ICAM)-1, respectively. We have reported previously that extracellular adherence protein (Eap) of Staphylococcus aureus exerts antiinflammatory activities by interacting with ICAM-1 and blocking beta2-integrin-dependent neutrophil recruitment. Here, we report that Eap inhibits experimental autoimmune encephalomyelitis (EAE) in mice. In vitro, Eap reduced adhesion of peripheral blood T cells to immobilized ICAM-1 as well as their adhesion and transmigration of TNF-activated human endothelium under static and shear flow conditions. These inhibitory effects were corroborated in two mouse models of inflammation. In a delayed-type hypersensitivity model, both T cell infiltration and the corresponding tissue edema were significantly reduced by Eap. In addition, Eap administration prevented the development of EAE and markedly decreased infiltration of inflammatory cells into the CNS. Strikingly, intervention with Eap after the onset of EAE suppressed the disease. Collectively, our findings indicate that Eap represents an attractive treatment for autoimmune neuroinflammatory disorders such as MS.

Amino Acid Sequence↗
PubMed2006

Crystallization and X-ray diffraction analysis of the complement component-3 (C3) inhibitory domain of Efb from Staphylococcus aureus.

The extracellular fibrinogen-binding protein (Efb) of Staphylococcus aureus is a multifunctional virulence factor capable of potent inhibition of complement component-3 (C3) activity in addition to its previously described fibrinogen-binding properties. A truncated recombinant form of Efb (Efb-C) that binds C3 has been overexpressed and purified and has been crystallized using the hanging-drop vapor-diffusion technique. Crystals of native Efb-C grew in the tetragonal space group P4(3) (unit-cell parameters a = b = 59.53, c = 46.63 A) with two molecules in the asymmetric unit and diffracted well beyond 1.25 A limiting Bragg spacing. To facilitate de novo phasing of the Efb-C crystals, two independent site-directed mutants were engineered in which either residue Ile112 or Val140 was replaced with methionine and crystals isomorphous to those of native Efb-C were reproduced using a seleno-L-methionine-labeled form of each mutant protein. Multiwavelength anomalous diffraction (MAD) data were collected on both mutants and analyzed for their phasing power toward solution and refinement of a high-resolution Efb-C crystal structure.

Bacterial Proteins↗
PubMed2005

An optimized system for expression and purification of secreted bacterial proteins.

In this report, we describe an optimized system for the efficient overexpression, purification, and refolding of secreted bacterial proteins. Candidate secreted proteins were produced recombinantly in Escherichia coli as Tobacco Etch Virus protease-cleavable hexahistidine-c-myc eptiope fusion proteins. Without regard to their initial solubility, recombinant fusion proteins were extracted from whole cells with guanidium chloride, purified under denaturing conditions by immobilized metal affinity chromatography, and refolded by rapid dilution into a solution containing only Tris buffer and sodium chloride. Following concentration on the same resin under native conditions, each protein was eluted for further purification and/or characterization. Preliminary studies on a test set of 12 secreted proteins ranging in size from 13 to 130 kDa yielded between 10 and 50 mg of fusion protein per liter of induced culture at greater than 90% purity, as judged by Coomassie-stained SDS-PAGE. Of the nine proteins further purified, analytical gel filtration chromatography indicated that each was a monomer in solution and circular dichroism spectroscopy revealed that each had adopted a well-defined secondary structure. While there are many potential applications for this system, the results presented here suggest that it will be particularly useful for investigators employing structural approaches to understand protein function, as attested to by the crystal structures of three proteins purified using this methodology (B.V. Geisbrecht, B.Y. Hamaoka, B. Perman, A. Zemla, D.J. Leahy, J. Biol. Chem. 280 (2005) 17243-17250).

Amino Acid Sequence↗
PubMed2005

Design and optimization of a recombinant system for large-scale production of the MPT64 antigen from Mycobacterium tuberculosis.

Early clinical trials of a potential new tuberculosis (TB) diagnostic, the Patch Test for Active TB (PTAT), used MPB64 protein that was purified from the spent medium of Bacillus Calmette-Guérin (BCG) Tokyo 172 vaccine production. The yield was poor, 0.05 mg/L, and the process for purification of the protein was complex, requiring four chromatographic steps. The combination of yield and purification complexity compromised the ability to produce the PTAT diagnostic in quantities sufficient for larger clinical trials and commercialization. We report here a highly efficient method for the overexpression and purification of recombinant MPT64 from Escherichia coli (rMPT64) based upon a mild insolubility of rMPT64 following induction, and scalable anion-exchange and gel filtration chromatographies. Yields of protein were improved substantially to approximately 250 mg/L, and resulted in a preparation greater than 98% pure. Quantitative release assays were developed and used with MALDI-TOF mass spectrometry to confirm the identity of rMPT64. Using a guinea pig model of active TB, we found that rMPT64 elicited a specific immune response indistinguishable from that of MPB64 purified from BCG Tokyo culture filtrates. These results describe the first efficient and scalable protocol for production of rMPT64, demonstrate its activity in an animal model of active TB, and lay the foundation of ongoing and future use of the PTAT in clinical settings.

Amino Acid Sequence↗
PubMed2005

The crystal structures of EAP domains from Staphylococcus aureus reveal an unexpected homology to bacterial superantigens.

The Eap (extracellular adherence protein) of Staphylococcus aureus functions as a secreted virulence factor by mediating interactions between the bacterial cell surface and several extracellular host proteins. Eap proteins from different Staphylococcal strains consist of four to six tandem repeats of a structurally uncharacterized domain (EAP domain). We have determined the three-dimensional structures of three different EAP domains to 1.8, 2.2, and 1.35 A resolution, respectively. These structures reveal a core fold that is comprised of an alpha-helix lying diagonally across a five-stranded, mixed beta-sheet. Comparison of EAP domains with known structures reveals an unexpected homology with the C-terminal domain of bacterial superantigens. Examination of the structure of the superantigen SEC2 bound to the beta-chain of a T-cell receptor suggests a possible ligand-binding site within the EAP domain (Fields, B. A., Malchiodi, E. L., Li, H., Ysern, X., Stauffacher, C. V., Schlievert, P. M., Karjalainen, K., and Mariuzza, R. (1996) Nature 384, 188-192). These results provide the first structural characterization of EAP domains, relate EAP domains to a large class of bacterial toxins, and will guide the design of future experiments to analyze EAP domain structure/function relationships.

Amino Acid Sequence↗
PubMed2004

Crystal structure of Caenorhabditis elegans HER-1 and characterization of the interaction between HER-1 and TRA-2A.

HER-1 is a secreted protein that promotes male development in the nematode Caenorhabditis elegans. HER-1 inhibits the function of TRA-2A, a multipass integral membrane protein thought to serve as its receptor. We report here the 1.5-A crystal structure of HER-1. The structure was solved by the multiwavelength anomalous diffraction method by using selenomethionyl-substituted HER-1 produced in Chinese hamster ovary cells. The HER-1 structure consists of two all-helical domains and is not closely homologous to any known structure. Sites of amino acid substitutions known to impair HER-1 function were mapped on the HER-1 structure and classified according to the likely mechanism by which they affect HER-1 activity. A subset of these and other amino acid substitutions on the HER-1 surface were assayed for their ability to disrupt interactions between HER-1 and TRA-2A-expressing cells, and a localized region on the HER-1 surface important for mediating this interaction was identified.

Amino Acid Sequence↗
PubMed2003

Netrin binds discrete subdomains of DCC and UNC5 and mediates interactions between DCC and heparin.

Netrins are secreted proteins that elicit both attractive and repulsive responses in migrating cells in the central and peripheral nervous systems. Netrins interact with members of two distinct families of transmembrane receptors, represented by DCC (deleted in colorectal cancer) and UNC5. A human netrin fragment (soluble netrin; sNetrin) was purified from an engineered Chinese hamster ovary cell line and used in a pull-down assay to map the interactions between netrin and its receptors. We find that sNetrin binds exclusively to the fifth fibronectin type III repeat of DCC and to each immunoglobulin repeat of UNC5. Both DCC and UNC5 bind to sNetrin with 1:1 stoichiometry in solution, and the minimal receptor fragments behave similarly to larger fragments in cross-linking experiments with purified sNetrin. We find no evidence for formation of a ternary complex between sNetrin and soluble forms of DCC and UNC5. We also find no evidence for an interaction between DCC and heparin and instead demonstrate that a loop on the fifth fibronectin type III repeat of DCC previously implicated in mediating interactions with heparin is important for sNetrin binding. Since netrin binds heparin, our results suggest that interactions between DCC and heparin are probably mediated by netrin.

Algorithms↗
PubMed2003

Correlating structure and affinity for PEX5:PTS1 complexes.

Many proteins that are destined to reside within the lumen of the peroxisome contain the peroxisomal targeting signal-1 (PTS1), a C-terminal tripeptide approximating the consensus sequence -Ser-Lys-Leu-COO(-). The PTS1 is recognized by the tetratricopeptide repeat (TPR) domains of PEX5, a cytosolic receptor that cycles between the cytoplasm and the peroxisome. To gain insight into the energetics of PTS1 binding specificity and to correlate these with features from the recently determined structure of a PEX5:PTS1 complex, we used a fluorescence-based binding assay that enables the quantitation of the dissociation constants for PTS1-containing peptide complexes with the TPR region of human PEX5. Through application of this assay to a collection of pentapeptides containing different C-terminal tripeptide sequences, including both natural and unnatural amino acids, the thermodynamic effects of sequence variation were examined. PTS1 variants that correspond to known functional targeting signals bind to the PEX5 fragment with a change in the standard binding free energy within 1.8 kcal mol(-1) of that corresponding to the peptide ending with -Ser-Lys-Leu-COO(-). The results suggest that a binding energy threshold may determine the functionality of PTS1 sequences.

Amino Acid Substitution↗
PubMed2002

Functional characterization of Delta3,Delta2-enoyl-CoA isomerases from rat liver.

The degradation of unsaturated fatty acids by beta-oxidation involves Delta(3),Delta(2)-enoyl-CoA isomerases (enoyl-CoA isomerases) that catalyze 3-cis --> 2-trans and 3-trans --> 2-trans isomerizations of enoyl-CoAs and the 2,5 --> 3,5 isomerization of dienoyl-CoAs. An analysis of rat liver enoyl-CoA isomerases revealed the presence of a monofunctional enoyl-CoA isomerase (ECI) in addition to mitochondrial enoyl-CoA isomerase (MECI) in mitochondria, whereas peroxisomes contain ECI and multifunctional enzyme 1 (MFE1). Thus ECI, which previously had been described as peroxisomal enoyl-CoA isomerase, was found to be present in both peroxisomes and mitochondria. This enzyme seems to be identical with mitochondrial long-chain enoyl-CoA isomerase (Kilponen, J.M., Palosaari, P.M., and Hiltunen, J.K. 1990. Biochem. J. 269, 223-226). All three hepatic enoyl-CoA isomerases have broad chain length specificities but are distinguishable by their preferences for one of the three isomerization reactions. MECI is most active in catalyzing the 3-cis --> 2-trans isomerization; ECI has a preference for the 3-trans --> 2-trans isomerization, and MFE1 is the optimal isomerase for the 2,5 --> 3,5 isomerization. A functional characterization based on substrate specificities and total enoyl-CoA isomerase activities in rat liver leads to the conclusion that the 3-cis --> 2-trans and 2,5 --> 3,5 isomerizations in mitochondria are catalyzed overwhelmingly by MECI, whereas ECI contributes significantly to the 3-trans --> 2-trans isomerization. In peroxisomes, ECI is predicted to be the dominant enzyme for the 3-cis --> 2-trans and 3-trans --> 2-trans isomerizations of long-chain intermediates, whereas MFE1 is the key enzyme in the 2,5 --> 3,5 isomerization.

Animals↗