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R Graff

Publications and source records attributed to R Graff.

14 recordsLinked to original sources
PubMed2005

The structure-activity relationship of ferric pyoverdine bound to its outer membrane transporter: implications for the mechanism of iron uptake.

Under iron limitation, Pseudomonas aeruginosa ATCC 15692 secretes a major siderophore, pyoverdine I (PvdI). This molecule chelates iron in the extracellular medium and shuttles it into the cells via a specific outer membrane transporter, FpvAI. PvdI consists of a fluorescent chromophore derived from 2,3-diamino-6,7-dihydroxyquinoline and containing one of the bidentate groups involved in iron chelation, linked to a peptide moiety containing the two other bidentate groups required for binding to Fe(3+). Kinetic studies, based on the fluorescence properties of this siderophore, showed that pH 8.0 was optimal for the binding of PvdI and PvdI-Fe to FpvAI. We investigated the mechanism of interaction of PvdI and PvdI-Fe with FpvAI, by synthesizing various analogues of this siderophore, determining their affinity for FpvAI in vitro and in vivo and their ability to transport iron, and interpreting the results obtained in light of the structure of FpvAI-PvdI. Our findings demonstrate that the succinyl moiety linked to the chromophore of PvdI and the first amino acid of the peptide moiety can be sterically hindered with no effect on binding or the iron uptake properties of PvdI-Fe. Moreover, the sequence and the structure of the peptide moiety of PvdI seems to be more important for the iron uptake step than for the binding of the siderophore to FpvAI. Finally, the efficiency of iron uptake and of recycling of the various PvdI analogues after iron release suggests that iron dissociates from PvdI on FpvAI or in the periplasm. All these data have serious implications for the specificity and mechanism of PvdI-mediated iron transport in P. aeruginosa.

Bacterial Outer Membrane Proteins↗
PubMed1996

Partially modified retro-inverso pseudopeptides as non-natural ligands for the human class I histocompatibility molecule HLA-A2.

Syntheses of a series of partially modified retro-inverso analogues of the antigenic peptide M58-66 derived from the influenza virus matrix protein are reported. The retro-inverso modification phi(NH-CO) was obtained by replacement of two successive amino acid residues with a 2-substituted malonate derivative and gem-diaminoalkyl residue. The resulting compounds 1-8 were tested for their binding to the human histocompatibility class I molecule HLA-A2 in an assembly assay using lysates of peptide transporter-deficient cells T2. Specific peptide-dependent HLA-A2 assembly was revealed by an enzyme-linked immunosorbent assay. Significant HLA-A2 assembly was detected in the presence of analogues [gGly58-(S)mLeu59]-M58-66 (1a), [gGly61-(R,S)mPhe62]M58-66 (4), [gVal63-(R,S)mPhe64]M58-66 (6), and [gPhe64-(R,S)mAla65]M58-66 (7). The introduction of the retro-inverso modification between P2-P3, P3-P4, P5-P6, and P8-P9 (compounds 2, 3, 5, and 8, respectively) however led to a dramatic reduction in peptide binding to HLA-A2. Interestingly, compound 1a which contains modification between P1-P2 was found to be the most potent analogue, being able to retain the original HLA-A2 binding profile of the parent peptide M58-66. Taken together, these results and recent binding data obtained in the context of murine MHC class I molecule H-2Kd suggest that the incorporation of peptide bond surrogates in MHC class I-restricted epitopes is a useful approach to design molecules having both increased stability and high MHC-binding capacity. Depending on their agonist or antagonist effects at the T-cell receptor, such non-natural MHC ligands are likely to find many applications in the development of peptide-based vaccines or as potential therapeutic agents in the treatment of allergies and autoimmune diseases.

Amino Acid Sequence↗
PubMed1993

A revised strategy for cloning antibody gene fragments in bacteria.

The ability to clone and overexpress genes encoding mouse Fab (antigen-binding fragment) proteins in bacteria led to the development of a methodology which has the potential to replace traditional hybridoma technology [Huse et al., Science 246 (1989) 1275-1281]; however, several observations have suggested that clones with desirable chemical properties may be missed in immunoscreens of large combinatorial libraries due to low levels of functional Ab protein. To increase the efficiency of cloning and characterization of Ab gene fragments, we have reconsidered several features of the original cloning vehicles. These studies show that at the present time a unique expression system cannot adequately accommodate the requirements of plaque-lift immunoassays for clonal selection and biochemical assays for further characterization in vitro. A monocistronic arrangement of heavy- and light-chain-encoding genes using two lacP promoters produces sufficient amounts of functional Ab protein for clonal selection from phage lambda libraries and minimizes interference with the lytic cycle of recombinant vectors. In liquid culture, a strong coliphage promoter and a relatively abundant RNA polymerase can be used to produce quantities of Ab protein sufficient for further characterization in vitro. A rapid purification protocol obviates the need for fusing heavy-chain protein to a decapeptide sequence, an affinity-tail sequence which slows the folding and assembly of the Ig heterodimer. These results have been used to formulate a new strategy for cloning and characterization of Ab gene fragments in bacteria.

Amino Acid Sequence↗
PubMed1993

The serine protease cofactor factor V is synthesized by lymphocytes.

Ag-specific cellular immune responses result in CD4+ T cell activation, which can induce the expression of tissue factor in cells of monocyte/macrophage lineage. This results in initiation of the coagulation protease cascade, with ultimate generation of thrombin. The latter is a potent and pleiotropic mediator of cellular responses and deposition of fibrin. To explore the requirements for extravascular cellular mediation of immune effector pathways, we have searched for a cellular source of the cofactor factor Va. Factor V mRNA was identified in human lymphoid cells by using reverse transcription followed by the polymerase chain reaction (RT-PCR). We confirmed our reverse transcription-polymerase chain reaction results by an independent cloning of factor V cDNA from a T cell cDNA library. The sequence of the factor V cDNA was virtually identical to hepatic factor V mRNA sequence. A limited span of mRNA, encoding part of the connecting region of the factor V protein, was found to contain nucleotide polymorphisms based on six nucleotide substitutions. Northern blot analysis confirmed the presence of a approximately 7-kb factor V mRNA in the Hut-78* human T lymphoma cell line and, at five- to eightfold less abundance, in unstimulated lymphocytes and long term allogeneic stimulated T cells. Immunocytology with factor V mAb identified factor V intracellularly in freshly isolated T lymphocytes but not on the surface of cells. These data provide evidence for factor V transcription and biosynthesis by human lymphocytes. They provide an additional perspective on how lymphocytes may contribute to inflammatory effector functions of cellular immune responses in extravascular sites through provision of cofactors necessary for the coagulation serine protease cascade.

Amino Acid Sequence↗
PubMed1992

Human combinatorial antibody libraries to hepatitis B surface antigen.

Human antibody Fab fragments that bind to hepatitis B surface antigen (HBsAg) were generated by using a recombinant phage surface-display expression system. Characterization of HBsAg-specific Fab fragments isolated from two vaccinated individuals reveals diversity in specificity of antigen binding and in the sequences of the complementarity-determining region. The sequence results show examples of human light-chain promiscuity that result in fine specificity changes and a strong relationship to a human germ-line gene. This application illustrates further that this technique is a powerful tool to isolate distinct human antibodies against immunogenic viral targets.

Amino Acid Sequence↗
PubMed1990

In vivo tests of the concept of photodynamic threshold dose in normal rat liver photosensitized by aluminum chlorosulphonated phthalocyanine.

In its simplest form, the photodynamic therapy (PDT) threshold dose model states that tissue necrosis due to PDT will occur if the number of photons absorbed by the photosensitizer per unit volume of tissue exceeds a critical value. This threshold is given by the product of photon fluence, photosensitizer concentration and specific absorption coefficient. To test the validity of this concept for PDT of normal rat liver sensitized with aluminum chlorosulphonated phthalocyanine (AISPC), all three of these parameters were varied by changing the injected AISPC dose, the wavelength of excitation and the irradiation geometry. The extent of necrosis caused by the treatment was consistent with the threshold model, except when the concentration of AISPC in the liver exceeded 20 micrograms g-1. For this animal model, we estimate the threshold to be (3.8 +/- 0.2) x 10(19) photons cm-3.

Animals↗
PubMed1983

Short term augmentation of amphetamine-induced rotation bias.

Using measures of stereotypy such as rearing, licking, and chewing, low dosage administration of amphetamine can be shown to produce increased stereotypy over a period of days. In the present study amphetamine-induced perservation was observed in two sessions when rotational behaviors were used as a behavioral measure. Rotational perseveration occurred in animals receiving both drug and testing experience in session one and session two. Animals receiving either drug or testing experience in session one did not show perseveration with drug and testing experience in session two.

Animals↗
PubMed1976

Aggressive management of genitourinary complications of renal transplantation.

In the course of 184 renal transplantations performed in St. Louis since 1963, twenty-six minor and twenty-three major complications have occurred. As a result of these complications four kidneys have been lost and 1 patient has died. Aggressive therapy has been utilized in the management of all but two of the major complications and is associated with one death and the loss of two kidneys. On the basis of these results intensive therapy for genitourinary complications is encouraged, and the principles of therapy are discussed.

Adult↗
PubMedDate not supplied

Synthesis and antigenic properties of reduced peptide bond pseudopeptide analogues of a histone H3 hexapeptide.

Pseudopeptide analogues of the C-terminal hexapeptide of histone H3 (-Ile-Arg-Gly-Glu-Arg-Ala-OH) were obtained by systematically replacing, in each analogue, one peptide bond at a time by a reduced peptide bond psi (CH2-NH). The resulting analogues were then examined, in ELISA and in the BIAcore system, for their ability to bind polyclonal and monoclonal antibodies generated against the parent natural peptide and the protein. The comparative results show that reduced bond pseudopeptide analogues can mimic the parent peptide. These results present the first unequivocal example for the potent applicability of reduced peptide bond pseudopeptides in the immunological field.

Amino Acid Sequence↗