Catalytic domains of tyrosine kinases determine the phosphorylation sites within c-Cbl

Catalytic (SH1) domains of protein tyrosine kinases (PTKs) demonstrate specificity for peptide substrates. Whether SH1 domains differentiate between tyrosines in a physiological substrate has not been confirmed. Using purified proteins, we studied the ability of Syk, Fyn, and Abl to differentiate between tyrosines in a common PTK substrate, c-Cbl. We found that each kinase produced a distinct pattern of c-Cbl phosphorylation, which altered the phosphotyrosine-dependent interactions between c-Cbl and CrkL or phosphatidylinositol 3'-kinase (PI3-K). Our data support the concept that SH1 domains determine the final sites of phosphorylation once PTKs reach their target proteins.     

Amphipathic peptides and drug delivery

The discovery of cell-penetrating peptides as gene delivery systems and the interest in the mechanism by which these vectors cross the cell membrane have generated a large number of studies. Among the parameters involved in the translocation process, controversy has arisen about the role of the amphipathicity of the carriers in the interaction and reorganization of the cell membrane. In this review we have summarized the vectors with primary or secondary amphipathicity related to secondary structure. Some of the insights into the relationship between the aggregation state of the peptide at the concentrations used for internalization studies and its interaction with the cell membrane result from our contribution to the field with a new family of amphipathic proline-rich peptides.     

Current knowledge of iron metabolism

Iron plays many roles in human physiology. In this article, we summarize the basic and current knowledge of this essential micronutrient on human metabolism.     

Thermotolerance requires refolding of aggregated proteins by substrate translocation through the central pore of ClpB

Cell survival under severe thermal stress requires the activity of the ClpB (Hsp104) AAA+ chaperone that solubilizes and reactivates aggregated proteins in concert with the DnaK (Hsp70) chaperone system. How protein disaggregation is achieved and whether survival is solely dependent on ClpB-mediated elimination of aggregates or also on reactivation of aggregated proteins has been unclear. We engineered a ClpB variant, BAP, which associates with the ClpP peptidase and thereby is converted into a degrading disaggregase. BAP translocates substrates through its central pore directly into ClpP for degradation. ClpB-dependent translocation is demonstrated to be an integral part of the disaggregation mechanism. Protein disaggregation by the BAP/ClpP complex remains dependent on DnaK, defining a role for DnaK at early stages of the disaggregation reaction. The activity switch of BAP to a degrading disaggregase does not support thermotolerance development, demonstrating that cell survival during severe thermal stress requires reactivation of aggregated proteins.     

Scavenging of photogenerated oxidative species by antimuscarinic drugs: atropine and derivatives

The quenching ability of photogenerated oxidative species by some antimuscarinic drugs generically named atropines (e.g. atropine [I] eucatropine [II], homatropine [III] and scopolamine [IV]) have been investigated employing stationary photolysis, polarographic detection of dissolved oxygen, stationary and time-resolved fluorescence spectroscopy, and laser flash photolysis. Using Rose Bengal as a dye sensitiser for singlet molecular oxygen, O(2)((1)Delta(g)), generation, compounds I-IV behave as moderate chemical plus physical quenchers of the oxidative species. Correlation between kinetic and electrochemical data indicates that the process is possibly driven by a charge-transfer interaction. The situation is somewhat more complicated employing the natural pigment riboflavin (Rf) as a sensitiser. Compounds I and II complex Rf ground state, diminishing the quenching ability towards singlet and triplet excited state of the pigment. On the other hand, compounds III and IV effectively quench Rf excited states, protecting the pigment against photodegradation. Under anaerobic conditions, semireduced Rf (Rf(.-)) is formed through quenching of excited triplet Rf. Nevertheless, although Rf(.-) is a well-known generator of the reactive species superoxide radical anion by reductive quenching in the presence of oxygen, the process of O(2)((1)Delta(g)) production prevails over superoxide radical generation, due to the relatively low rate constants for the quenching of triplet Rf by the atropines (in the order of 10(7) M(-1)s(-1) for compounds III and IV) in comparison to the rate constant for the quenching by ground state oxygen, approximately two orders of magnitude higher, yielding O(2)((1)Delta(g)). Compound I is the most promising O(2)((1)Delta(g)) physical scavenger, provided that it exhibits the higher value for the overall quenching rate constant and only 11% of the quenching process leads to its own chemical damage.     

The negative systemic effect of BCGcw inoculated intraperitoneally

Summary The present studies describe a systemic effect of BCGcw inoculated intraperitoneally by observing its influence on the development of Morris hepatomas inoculated intramuscularly. In none of our studies did we observe an inhibition of tumor growth. Instead, an enhancement of tumor growth was seen with four antigenically distinct Morris hepatomas (3924a, 9098, 7777, and 5123tc) in two strains of inbred rats (Buffalo and ACI). Extensive studies with Morris hepatoma 3924a showed consistent enhancement of intramuscular tumor growth in eight of eight experiments with a tumor cell dose of 1×10⁵ and a BCGcw dose of 900 g. In BCGcw-inoculated animals, palpable tumors (1–2 g) were detected approximately 1 week earlier than in controls, and significantly larger tumor masses were noted on the day of sacrifice. With the threshold dose of cells, 1×10⁴, an increase in tumor incidence was observed. It was not necessary for the host to be immunized with BCGcw prior to tumor inoculation as enhancement of tumor growth occurred when the BCGcw were inoculated the same day or 7 days after tumor inoculation. Splenectomized animals also demonstrated BCGcw-mediated enhancement of tumor growth. BCGcw immunization blocks the induction of tumor-specific immunity. When 3924a ascites tumor cells were inoculated intradermally into normal animals, no tumor growth was observed and tumor-specific immunity resulted. When 3924a ascites tumor cells were inoculated intradermally into BCGcw-immunized animals, progressive intradermal tumors grew in all the animals, implying that tumor-specific immunity was not induced. The administration of BCGcw did not effect established tumor-specific immunity to line 3924a as assessed by tumor-specific rechallenge resistance. Studies with an allograft system showed that the ACI tumor 3924a would not grow in normal Buffalo rats, but transient tumor growth was observed when the Buffalo rats were immunized with BCGcw. The abbreviations used are: BCGcw, bacillus Calmette-Guérin cell walls attached to oil droplets; MLC, mixed lymphocyte culture; MER, methanol extract residue; IM, intramuscular; IP, intraperitoneal; ID, intradermal; Con-A, concanavalin-A     

<Emphasis Type="Italic">rpoS</Emphasis> Gene Expression in Carbon-Starved Cultures of the Polyhydroxyalkanoate-Accumulating Species <Emphasis Type="Italic">Pseudomonas oleovorans</Emphasis>

The expression of the rpoS gene during PHA depolymerization was monitored in Pseudomonas oleovorans GPo1 and its mutant defective in PHA degradation by analyzing the tolerance to oxidative and thermal stresses and the RpoS intracellular content. An increase in the tolerance to H₂O₂ and heat shock was observed coincidentally with PHA degradation. Western blotting experiments performed in carbon-starved cultures showed that the RpoS levels were higher in the wild type than in the mutant strain. Complementation of the phaZ mutation restores the wild-type RpoS levels. These results suggest a probable association between PHA depolymerization and the stress tolerance phenotype controlled by RpoS.     

Identifying and characterising the Plasmodium falciparum merozoite surface protein 10 Plasmodium vivax homologue

Plasmodium vivax malaria is one of the most prevalent parasitic diseases in Asia and Latin-America. The difficulty of maintaining this parasite culture in vitro has hampered identifying and characterising proteins implied in merozoite invasion of red blood cells. We have been able to identify an open reading frame in P. vivax encoding the Plasmodium falciparum merozoite surface protein 10 homologous protein using the partial sequences from this parasite's genome reported during 2004. This new protein contains 479 amino-acids, two epidermal growth factor-like domains, hydrophobic regions at the N- and C-termini, being compatible with a signal peptide and a glycosylphosphatidylinositol anchor site, respectively. The protein is expressed during the parasite's asexual stage and is recognised by polyclonal sera in parasite lysate using Western blot. P. vivax-infected patients' sera highly recognised recombinant protein by ELISA.     

Decoding the entry of two novel cell-penetrating peptides in HeLa cells: lipid raft-mediated endocytosis and endosomal escape

Cellular entry of peptide, protein, and nucleic acid biopharmaceuticals is severely impeded by the cell membrane. Linkage or assembly of such agents and cell-penetrating peptides (CPP) with the ability to cross cellular membranes has opened a new horizon in biomedical research. Nevertheless, the uptake mechanisms of most CPP have been controversially discussed and are poorly understood. We present data on two recently developed oligocationic CPP, the sweet arrow peptide SAP, a gamma-zein-related sequence, and a branched human calcitonin derived peptide, hCT(9-32)-br, carrying a simian virus derived nuclear localization sequence in the side chain. Uptake in HeLa cells and intracellular trafficking of N-terminally carboxyfluorescein labeled peptides was studied by confocal laser scanning microscopy and flow cytometry using biochemical markers in combination with quenching and colocalization approaches. Both peptides were readily internalized by HeLa cells through interaction with the extracellular matrix followed by lipid raft-mediated endocytosis as confirmed by reduced uptake at lower temperature, in the presence of endocytosis inhibitors and through cholesterol depletion by methyl-beta-cyclodextrin, supported by colocalization with markers for clathrin-independent pathways. In contrast to the oligocationic SAP and hCT(9-32)-br, interaction with the extracellular matrix, however, was no prerequisite for the observed lipid raft-mediated uptake of the weakly cationic, unbranched hCT(9-32). Transient involvement of endosomes in intracellular trafficking of SAP and hCT(9-32)-br prior to endosomal escape of both peptides was revealed by colocalization and pulse-chase studies of the peptides with the early endosome antigen 1. The results bear potential for CPP as tools for intracellular drug delivery.