Estudos dos efeitos de carga e da hidrofobicidade na interação de peptídeos antimicrobianos e membranas modelo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da conformação e atividade lítica de peptídeos antimicrobianos de vespas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudos conformacionais por dinâmica molecular de peptídeos antimicrobianos da família dos Mastoparanos em misturas de TFE-água

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estrutura e função de mastoparanos dos venenos de vespas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of the aspartic acid D2 on the affinity of Polybia-MP1 to anionic lipid vesicles

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The effects of the C-terminal amidation of mastoparans on their biological actions and interactions with membrane-mimetic systems

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudos das interações do peptídeo antimicrobiano Polybia MP1 com membranas modelo: mecanismo de ação e especificidade

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Proteômica como estratégia para estudos dos mecanismos de ativação de mastócitos de ratos causados pelo peptídeo Protopolybia MP-III

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Production of Human Antibody Fragments Binding to Melittin and Phospholipase A2 in Africanised Bee Venom: Minimising Venom Toxicity

The hybrid created from the crossbreeding of European and African bees, known as the Africanised bee, has provided numerous advantages for current beekeeping. However, this new species exhibits undesirable behaviours, such as colony defence instinct and a propensity to attack en masse, which can result in serious accidents. To date, there is no effective treatment for cases of Africanised bee envenomation. One promising technique for developing an efficient antivenom is the use of phage display technology, which enables the production of human antibodies, thus avoiding the complications of serum therapy, such as anaphylaxis and serum sickness. The aim of this study was to produce human monoclonal single-chain Fv (scFv) antibody fragments capable of inhibiting the toxic effects of Africanised bee venom. We conducted four rounds of selection of antibodies against the venom and three rounds of selection of antibodies against purified melittin. Three clones were selected and tested by enzyme-linked immunosorbent assay to verify their specificity for melittin and phospholipase A2. Two clones (C5 and C12) were specific for melittin, and one (A7) was specific for phospholipase A2. In a kinetic haemolytic assay, these clones were evaluated individually and in pairs. The A7-C12 combination had the best synergistic effect and was chosen to be used in the assays of myotoxicity inhibition and lethality. The A7-C12 combination inhibited the in vivo myotoxic effect of the venom and increased the survival of treated animals.

Gi regulation of secretory vesicle swelling examined by atomic force microscopy

In the last decade, several monomeric and heterotrimeric guanine nucleotide binding proteins have been identified to associate with secretory vesicles and to be implicated in exocytosis. Vesicle volume also has been proposed to play a regulatory role in secretory vesicle fusion at the plasma membrane. However, the molecular mechanism of function of the guanine nucleotide binding proteins and of the regulation of secretory vesicle volume in the exocytotic process remains unclear. In this study, we report association of the secretory vesicle membrane with the α subunit of a heterotrimeric GTP binding protein Gαi3 and implicate its involvement in vesicle swelling. Using an atomic force microscope in combination with confocal microscopy, we were able to study the dynamics of isolated zymogen granules, the secretory vesicles in exocrine pancreas. Exposure of zymogen granules to GTP resulted in a 15–25% increase in vesicle height as measured by the atomic force microscope and a similar increase in vesicle diameter as determined by confocal microscopy. Mas7, an active mastoparan analog known to stimulate Gi proteins, was found to stimulate the GTPase activity of isolated zymogen granules and cause swelling. Increase in vesicle size in the presence of GTP, NaF, and Mas7 were irreversible and KCl-sensitive. Ca2+ had no effect on zymogen granule size. Taken together, the results indicate that Gαi3 protein localized in the secretory vesicle membrane mediates vesicle swelling, a potentially important prerequisite for vesicle fusion at the cell plasma membrane.

Interaction of Fibroblast Growth Factor-2 (FGF-2) with Free Gangliosides: Biochemical Characterization and Biological Consequences in Endothelial Cell Cultures

Exogenous gangliosides affect the angiogenic activity of fibroblast growth factor-2 (FGF-2), but their mechanism of action has not been elucidated. Here, a possible direct interaction of sialo-glycolipids with FGF-2 has been investigated. Size exclusion chromatography demonstrates that native, but not heat-denatured, 125I-FGF-2 binds to micelles formed by gangliosides GT1b, GD1b, or GM1. Also, gangliosides protect native FGF-2 from trypsin digestion at micromolar concentrations, the order of relative potency being GT1b > GD1b > GM1 = GM2 = sulfatide > GM3 = galactosyl-ceramide, whereas asialo-GM1, neuraminic acid, and N-acetylneuramin-lactose were ineffective. Scatchard plot analysis of the binding data of fluorochrome-labeled GM1 to immobilized FGF-2 indicates that FGF–2/GM1 interaction occurs with a Kd equal to 6 μM. This interaction is inhibited by the sialic acid-binding peptide mastoparan and by the synthetic fragments FGF-2(112–129) and, to a lesser extent, FGF-2(130–155), whereas peptides FGF-2(10–33), FGF-2(39–59), FGF-2(86–96), and the basic peptide HIV-1 Tat(41–60) were ineffective. These data identify the COOH terminus of FGF-2 as a putative ganglioside-binding region. Exogenous gangliosides inhibit the binding of 125I-FGF-2 to high-affinity tyrosine-kinase FGF-receptors (FGFRs) of endothelial GM 7373 cells at micromolar concentrations. The order of relative potency was GT1b > GD1b > GM1 > sulfatide a = sialo-GM1. Accordingly, GT1b,GD1b, GM1, and GM2, but not GM3 and asialo-GM1, prevent the binding of 125I-FGF-2 to a soluble, recombinant form of extracellular FGFR-1. Conversely, the soluble receptor and free heparin inhibit the interaction of fluorochrome-labeled GM1 to immobilized FGF-2. In agreement with their FGFR antagonist activity, free gangliosides inhibit the mitogenic activity exerted by FGF-2 on endothelial cells in the same range of concentrations. Also in this case, GT1b was the most effective among the gangliosides tested while asialo-GM1, neuraminic acid, N-acetylneuramin-lactose, galactosyl-ceramide, and sulfatide were ineffective. In conclusion, the data demonstrate the capacity of exogenous gangliosides to interact with FGF-2. This interaction involves the COOH terminus of the FGF-2 molecule and depends on the structure of the oligosaccharide chain and on the presence of sialic acid residue(s) in the ganglioside molecule. Exogenous gangliosides act as FGF-2 antagonists when added to endothelial cell cultures. Since gangliosides are extensively shed by tumor cells and reach elevated levels in the serum of tumor-bearing patients, our data suggest that exogenous gangliosides may affect endothelial cell function by a direct interaction with FGF-2, thus modulating tumor neovascularization.

N-Acylethanolamines: Formation and Molecular Composition of a New Class of Plant Lipids1

Recently, the biosynthesis of an unusual membrane phospholipid, N-acylphosphatidylethanolamine (NAPE), was found to increase in elicitor-treated tobacco (Nicotiana tabacum L.) cells (K.D. Chapman, A. Conyers-Hackson, R.A. Moreau, S. Tripathy [1995] Physiol Plant 95: 120–126). Here we report that before induction of NAPE biosynthesis, N-acylethanolamine (NAE) is released from NAPE in cultured tobacco cells 10 min after treatment with the fungal elicitor xylanase. In radiolabeling experiments [14C]NAE (labeled on the ethanolamine carbons) increased approximately 6-fold in the culture medium, whereas [14C]NAPE associated with cells decreased approximately 5-fold. Two predominant NAE molecular species, N-lauroylethanolamine and N-myristoylethanolamine, were specifically identified by gas chromatography-mass spectrometry in lipids extracted from culture medium, and both increased in concentration after elicitor treatment. NAEs were found to accumulate extracellularly only. A microsomal phospholipase D activity was discovered that formed NAE from NAPE; its activity in vitro was stimulated about 20-fold by mastoparan, suggesting that NAPE hydrolysis is highly regulated, perhaps by G-proteins. Furthermore, an NAE amidohydrolase activity that catalyzed the hydrolysis of NAE in vitro was detected in homogenates of tobacco cells. Collectively, these results characterize structurally a new class of plant lipids and identify the enzymatic machinery involved in its formation and inactivation in elicitor-treated tobacco cells. Recent evidence indicating a signaling role for NAPE metabolism in mammalian cells (H.H.O. Schmid, P.C. Schmid, V. Natarajan [1996] Chem Phys Lipids 80: 133–142) raises the possibility that a similar mechanism may operate in plant cells.

Structural determinants for binding to CGRP receptors expressed by human SK-N-MC and Col 29 cells:Studies with chimeric and other peptides

1. Structure-activity relationships for the binding of human α-calcitonin gene-related peptide 8-37 (hαCGRP8-37) have been investigated at the CGRP receptors expressed by human SK-N-MC (neuroblastoma) and Col 29 (colonic epithelia) cells by radioligand binding assays and functional assays (hαCGRP stimulation of adenylate cyclase). 2. On SK-N-MC cells the potency order was hαCGRP8-37 > hαCGRP19-37 = AC187 > rat amylin8-37 > hα[Tyr0]-CGRP28-37 (apparent pKBS of 7.49 ± 0.25, 5.89 ± 0.20, 6.18 ± 0.19, 5.85 ± 0.19 and 5.25 ± 0.07). The SK-N-MC receptor appeared CGRP1-like. 3. On Col 29 cells, only hαCGRP8-37 of the above compounds was able to antagonize the actions of hαCGRP (apparent pKB = 6.48 ± 0.28). Its receptor appeared CGRP2-like. 4. hα[Ala11,18]-CGRP8-37, where the amphipathic nature of the N-terminal α-helix has been reduced, bound to SK-N-MC cells a 100 fold less strongly than hαCGRP8-37. 5. On SK-N-MC cells, hαCGRP(8-18, 28-37) (M433) and mastoparan-hαCGRP28-37 (M432) had apparent pKBS of 6.64 ± 0.16 and 6.42 ± 0.26, suggesting that residues 19-27 play a minor role in binding. The physico-chemical properties of residues 8-18 may be more important than any specific side-chain interactions. 6. M433 was almost as potent as hαCGRP8-37 on Col 29 cells (apparent pKB = 6.17 ± 0.20). Other antagonists were inactive.