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Biomedical subjects

M Kahn

Publications and source records attributed to M Kahn.

At least 55 records · Page 3Linked to original sources
PubMed1994

Conformational rearrangements required of the V3 loop of HIV-1 gp120 for proteolytic cleavage and infection.

HIV gp120 is specifically cleaved at a single site in the V3 loop between Arg315 and Ala316 by thrombin. Previous observations by others have indicated that binding to CD4 enhances the rate of V3 loop cleavage, and that this cleavage is a prerequisite for HIV infection. Other observations also suggest that the cleavage site is in a type II beta-turn centered at Pro313-Gly314. However, our docking experiments indicate that this conformation cannot dock to thrombin and other trypsin-like serine proteases. Thus, based on the thrombin-bound conformation of peptide substrates, we propose that CD4 binding, at a site remote from the V3 loop, induces and stabilizes a trans to cis isomerization of the highly conserved residue Pro313, and that this conformational shift is a prerequisite for cleavage by a 'thrombin-like' cellular protease and subsequent infection.

Binding Sites↗
PubMed1994

Dual specificity of a monoclonal anti-idiotypic antibody for HIV-1 neutralizing monoclonals 110.3 and 110.4 as well as the V3 loop of gp120.

Monoclonal antibodies (MAbs) 110.3 and 110.4 bind an epitope at the tip of the third hypervariable region (V3) of the envelope protein gp120 of human immunodeficiency virus type 1 (HIV-1). These MAbs inhibit HIV-induced syncytium formation and neutralize cell-free virus infection. Anti-idiotypic MAb alpha-id8, generated against 110.3, was found to mimic the V3 loop of gp120, as demonstrated by competition ELISA and by the generation of anti-anti-idiotypic sera which bound gp120 and a peptide representing the tip of the V3 loop. Interestingly, alpha-id8 itself also reacted specifically with both gp120 and the V3 loop peptide. Thus, alpha-id8 both mimics and binds directly to the V3 loop, suggesting that the V3 loop of gp120 may associate with itself.

Amino Acid Sequence↗
PubMed1993

Peptidomimetics of the immunoglobulin supergene family--a review.

An important goal of structural biochemistry is the reduction of complex molecules to small functional units that are amenable to high-resolution structural analysis and rapid modification. The dissection of multidomain proteins into small synthetic conformationally restricted components is an important step in the design of low-molecular-weight nonpeptides that mimic the activity of the native protein. Mimetics of critical functional domains might possess beneficial properties in comparison to the intact proteinaceous species with regard to specificity and therapeutic potential, and are valuable probes for the study of molecular recognition events.

Drug Design↗
PubMed1993

Measurement and relationship of subarachnoid pressure of the optic nerve to intracranial pressures in fresh cadavers.

We performed a study on six fresh cadavers to measure the subarachnoid pressure of the optic nerve and to determine its relationship to intracranial pressure. A lateral orbitotomy via a coronal flap was used to expose the optic nerve. Various intracranial pressures were achieved by saline infusion through a ventriculostomy. The subarachnoid pressure of the optic nerve was measured at 5 and at 25 mm posterior to the globe under conditions of the created intracranial pressure. The effectiveness of optic nerve sheath decompression performed by two standardized surgical techniques was determined experimentally and by theoretic calculations; the role of the bulbous portion of the optic nerve was assessed experimentally. Measurements of the subarachnoid pressure of the optic nerve showed interindividual variation and a linear relationship with the intracranial pressure. Surgical decompression through a 3 x 5-mm window was more effective than were three linear 5-mm incisions. The bulbous portion of the optic nerve was found to have an important role in cerebrospinal fluid circulation.

Adult↗
PubMed1993

The regulation by light of retinal necrosis and the immune response following anterior chamber inoculation of herpes simplex virus type-1.

Following anterior chamber injection of the KOS strain of herpes simplex virus type 1 into Balb/c mice a characteristic pathologic response occurs. When examined 10-14 days later there is intense anterior segment inflammation of the injected eye, but the retina is spared. In contrast, the contralateral eye undergoes intense and destructive retinitis with little or no involvement of the anterior segment. Coincident with these observations is the induction of ACAID (for anterior chamber associated immune deviation) which is characterized by a suppressed DTH response, normal antibody titers, and normal cytolytic T-cell responses to HSV antigens. Since we have recently demonstrated that ACAID does not take place in the absence of light (i.e., is light dependent), we have examined the effect of light on the HSV-retinitis model. When Balb/c mice are either dark-reared or dark-adapted prior to AC injection of HSV-1, contralateral retinitis is abolished. Concurrent with the abrogation of retinitis, is the elimination of ACAID to HSV-1 antigens. In addition, although contralateral retinitis and ACAID do not develop in dark-reared mice if they are placed in the light immediately following injection, both can be re-established in dark-reared animals following a 2 week period of re-adaptation to light. Our results demonstrate that the entrance of light into the eye is not only important for ACAID, but also for the development of contralateral HSV-induced retinitis.

Animals↗
PubMed1993

Immunocytologic findings in a case of Vogt-Koyanagi-Harada syndrome.

BACKGROUND: Vogt-Koyanagi-Harada (VKH) syndrome is a form of chronic panuveitis that often has a poor long-term visual outcome. To the authors' knowledge, there have been only two previous reports describing immunocytologic findings in the eyes of patients with VKH syndrome, all studied in relatively late stages of the disease. METHODS: The authors performed immunocytologic studies on the enucleated eyes of a patient with active VKH syndrome, using monoclonal antibodies to mononuclear subsets, major histocompatibility antigens, and viral and treponemal agents, to better understand the pathophysiologic mechanisms underlying the disease. Emulsified chorioretinal tissue also was processed for viral isolation in tissue culture and for Treponema pallidum by rabbit inoculation studies. RESULTS: The dense uveal infiltrates in active VKH syndrome are composed predominantly of T lymphocytes and HLA-DR+ macrophages. Scattered T cells and plasma cells were present in the retina. In addition, nondendritic-appearing CD1 (Leu-6) positive cells were localized in the choroid, in close proximity to choroidal melanocytes. No microbial agents were identified. CONCLUSION: Whereas the etiology of the VKH syndrome remains an enigma, the authors' immunocytologic findings are consistent with a T-cell-mediated disorder. In demonstrating CD1 (Leu-6) positive cells in the infiltrates, the authors propose a potential role for these cells in the etiology of VKH syndrome.

Cell Count↗
PubMed1993

The structure of a designed peptidomimetic inhibitor complex of alpha-thrombin.

Thrombin displays remarkable specificity, effecting the removal of fibrinopeptides A and B of fibrinogen through the selective cleavage of two Arg-Gly bonds between the 181 Arg/Lys-Xaa bonds in fibrinogen. Significant advances have been made in recent years towards understanding the origin of the specificity of cleavage of the Arg16-Gly17 bond of the A alpha-chain of human fibrinogen. We have previously proposed a model for the bound structure of fibrinopeptide A7-16 (FPA), based upon NMR data, computer-assisted molecular modeling and the synthesis and study of peptidomimetic substrates and inhibitors of thrombin. We now report the structure of the ternary complex of an FPA mimetic (FPAM), hirugen and thrombin at 2.5 A resolution (R-factor = 0.138) and specificity data for the inhibition of thrombin and related trypsin-like proteinases by FPAM. The crystallographic structures of FPA and its chloromethyl ketone derivative bound to thrombin were determined. Although there are differences between these structures in the above modeled FPA structure and that of the crystal structure of FPAM bound to thrombin, the phi, psi angles in the critical region of P1-P2-P3 in all of the structures are similar to those of bovine pancreatic trypsin inhibitor (BPTI) in the BPTI-trypsin complex and D-Phe-Pro-Arg (PPACK) in the PPACK-thrombin structure. A comparison between these and an NMR-derived structure is carried out and discussed.

Amino Acid Chloromethyl Ketones↗
PubMed1992

Design, synthesis and conformational analysis of gamma-turn peptide mimetics of bradykinin.

Gamma-turns are regular secondary structure elements, found with some frequency in small peptides, that have been implicated in the biologically active conformations of several systems. This report describes the design, synthesis and conformational analysis of a non-peptide gamma-turn mimetic. Low energy conformations of the mimetic system exhibit good conformational agreement with an experimentally observed peptide gamma-turn. The mimetics were incorporated into the nonapeptide bradykinin, for which a gamma-turn, formed by residues Ser 6 to Phe 8, has been hypothesized to be a bioactive conformation. The results indicate that a bioactive conformation of bradykinin may include a reverse turn at this position.

Amino Acid Sequence↗
PubMed1992

Peptide mimetics of the thrombin-bound structure of fibrinopeptide A.

Recent work has suggested that the thrombin-bound conformation of fibrinopeptide A exhibits a strand-turn-strand motif, with a beta-turn centered at residues Glu-11 and Gly-12. Our molecular modeling analysis indicates that the published fibrinopeptide conformation cannot bind reasonably to thrombin but that reorientation of two residues by alignment with bovine pancreatic trypsin inhibitor provides a good fit within the deep thrombin cleft and satisfies all of the experimental nuclear Overhauser effect data. Based on this analysis, we have successfully designed and synthesized hybrid peptide mimetic substrates and inhibitors that mimic the proposed beta-turn structure. The results indicate that the turn conformation is an important aspect of thrombin specificity and that our turn mimetic design successfully mimics the thrombin-bound conformation of fibrinopeptide.

Amino Acid Sequence↗
PubMed1992

Human melanotransferrin (p97) has only one functional iron-binding site.

The iron-binding properties of melanotransferrin, the tumour-associated antigen also known as p97, have been investigated by UV/visible and fluorescence spectroscopy, amino acid sequence comparison, and modelling. These show that, in contrast to other transferrins, melanotransferrin binds only one Fe3+ ion per molecule. The binding properties of its N-terminal site are similar to other transferrins, but its C-terminal site does not bind iron at all. The differences can be related to specific amino acid changes in the C-terminal site.

Antigens, Neoplasm↗
PubMed1992

Polyreactive autoantibodies to negatively charged epitopes following Trypanosoma cruzi infection.

During the course of many human autoimmune diseases, antibodies which recognize negatively charged epitopes on self antigens are detected. Trypanosoma cruzi, an intracellular protozoan parasite capable of infecting a wide variety of vertebrates, is the cause of Chagas disease in humans. Infection with the parasite frequently results in autoimmune and inflammatory pathology. We report here on an affinity-purified population of antibodies that bind to a broad class of antigens that contain runs of acidic amino acids, including tubulin. Although these antibodies can be isolated from both uninfected and T. cruzi chronically infected C3H/He mice, the antibodies from the normal mice (the natural autoantibodies) bind to tubulin poorly at physiological pH, whereas the antibodies isolated from the infected animals bind well at physiological pH. We propose that similar processes may occur in humans following other infections accounting for the detection of antibodies to negatively charged epitopes in a variety of autoimmune diseases.

3T3 Cells↗
PubMed1992

Loops and secondary structure mimetics: development and applications in basic science and rational drug design.

One goal of protein design and structural biochemistry is the reduction of complex molecules to small functional units that are amenable to high resolution analysis and rapid modification. We have developed a variety of small molecules which biochemically and biologically mimic the combining sites of proteins of the immunoglobulin superfamily. The chemical and biological properties of peptide mimetics suggest that these analogs can be used as indicators for new pharmaceutical agents. Mimetics are powerful tools for the study of molecular recognition since they are small in size, maintain solubility in physiologic fluids and are amenable to detailed structural studies. As such, they represent a step toward the rational design of low molecular weight non-peptide pharmaceutical agents devoid of some of the shortcomings of conventional peptides. Here we discuss the rationale and approaches for the development of these molecules, and their current and future applications.

Amino Acid Sequence↗
PubMed1992

Effects of topical retinoids on cytoskeletal proteins: implications for retinoid effects on epidermal differentiation.

In vivo effects of retinoids on epidermal differentiation were investigated by analyzing cytoskeletal proteins in rhino mice treated topically with all-trans-retinoic acid (RA) and other retinoids (13-cis-retinoic acid, etretinate, TTNPB). Non-disulfide-linked cytoskeletal proteins, including keratins from the epidermal "living layers," were first selectively extracted using 9.5 M urea; subsequently, keratins of the stratum corneum were isolated using 9.5 M urea plus a reducing agent. Gel electrophoresis and immunoblot analysis showed that urea extracts of epidermis from vehicle-treated skin were composed predominantly of four major keratins (analogous to human epidermal keratins K1, K5, K10, and K14), and the keratin filament-associated protein filaggrin. In contrast, extracts of epidermis from retinoid-treated skin contained additional keratins (K6, K16, and K17) and almost no detectable filaggrin. Furthermore, similar analysis of stratum corneum keratins demonstrated that extracts from RA-treated skin did not contain the partially proteolyzed keratins typically observed in stratum corneum extracts of control animals. Hyperplasia-inducing agents (salicylic acid, croton oil) caused an increase in keratins K6, K16, and K17, but they did not effect filaggrin or alter proteolysis of stratum corneum keratins. The result that RA induced expression of keratins K6, K16, and K17, as commonly expressed in hyperproliferative epidermis, is consistent with the notion that retinoids increase epidermal cell proliferation in the basal and/or lower spinous layers. The findings that topical RA decreased filaggrin expression and reduced proteolysis of stratum corneum keratins, despite increased size and number of granular cells and the presence of an anucleate stratum corneum, suggest that topical RA may also modulate a later stage of epidermal differentiation involved in stratum corneum formation.

Administration, Topical↗
PubMed1991

Design and synthesis of a mimetic from an antibody complementarity-determining region.

A technique for producing non-peptide compounds (mimetics) of designed specificities was developed that permitted the synthesis of a conformationally restricted molecule that mimicked the binding and functional properties of monoclonal antibody (MAb) 87.92.6, which recognizes the reovirus type 3 cellular receptor. Binding of either MAb 87.92.6, peptide analogs, or 87.1-mimetic to the cellular receptor inhibited cellular proliferation. The mimetic was a synthetic beta-loop structure that mimics the second complementarity-determining region of the MAb. These studies may lead to strategies for the synthetic design of antibody complementarity regions, ligands, and other pharmacologically active agents that are water soluble, resistant to proteolysis, and nonimmunogenic.

Antibodies, Monoclonal↗
PubMed1991

CD4+ T cell clones specific for the human p97 melanoma-associated antigen can eradicate pulmonary metastases from a murine tumor expressing the p97 antigen.

p97 is a human tumor-associated Ag present on most melanoma cells that represents a possible target for immunologic attack. To evaluate the capacity of T cells reactive with this protein to promote elimination of melanoma cells expressing p97, a murine model was developed by transfecting a C3H/HeN melanoma with the p97 cDNA, generating p97-specific CD4+ T cells by in vivo immunization of C3H/HeN mice with a vaccinia/p97 recombinant virus followed by in vitro cloning with soluble p97 protein, and determining whether these CD4+ T cells could mediate rejection of pulmonary metastases. Characterization of the T cell clones demonstrated the presence of both I-Ak and I-Ek-restricted clones, although the majority of clones recognized p97 in the context of I-Ek. Analysis of clonal specificity using truncated p97 proteins revealed that at least three epitopes were immunogenic, and further studies with overlapping 15-amino acid peptides from a region of the p97 molecule defined by these truncated proteins identified an immunodominant epitope responsible for the majority of the I-Ek response. The T cell clones were not capable of directly recognizing the p97-expressing melanoma cells but responded to the tumor if syngeneic APC were present to process the tumor-derived p97 Ag. The therapeutic efficacy of these CD4+ T cell clones was evaluated in an adoptive therapy model in which mice bearing metastatic pulmonary lesions were treated by i.v. administration of the p97-specific cells. Despite the inability of the CD4+ clones to directly respond to or lyse the tumor cells, the clones were effective in promoting tumor eradication. In vitro studies demonstrated that this may have reflected secretion of lymphokines that activated macrophages to lyse the tumor. The results suggest that noncytolytic p97-specific CD4+ T cell clones can be effective in therapy of pulmonary melanoma metastases. Moreover, if human T cells reactive with the p97 protein could be generated, the expression of this tumor-associated Ag in melanoma cells might be adequate for such T cells to mediate a therapeutic antitumor response.

Animals↗