Biomedical subjects

Sergio Lizano

Publications and source records attributed to Sergio Lizano.

7 recordsLinked to original sources

PubMed2006

Population genetics and linkage analysis of loci within the FCT region of Streptococcus pyogenes.

The FCT regions of Streptococcus pyogenes strains encode a variety of cell wall-anchored surface proteins that bind the extracellular matrix of the human host and/or give rise to pilus-like appendages. Strong linkage is evident between transcription-regulatory loci positioned within the FCT and emm regions and the emm pattern genotype marker for preferred infection of the throat or skin. These findings provide a basis for the hypothesis that FCT region gene products contribute to tissue-specific infection. In an initial series of steps to address this possibility, the FCT regions of 13 strains underwent comparative sequence analysis, the gene content of the FCT region was characterized for 113 strains via PCR, and genetic linkage was assessed. A history of extensive recombination within FCT regions was evident. The emm pattern D-defined skin specialist strains were highly homogenous in their FCT region gene contents, whereas the emm pattern A-C-defined throat specialist strains displayed a greater variety of forms. Most pattern A-C strains harbored prtF1 (75%) but lacked cpa (75%). In contrast, the majority of emm pattern D strains had cpa (92%) but lacked prtF1 (79%). Models based on FCT and emm region genotypes revealed the most parsimonious pathways of evolution. Using niche-determining candidate genes to infer phylogeny, emm pattern E strains--the so-called generalists, which lack a strong tissue site preference--occupied a transition zone separating most throat specialists from skin specialists. Overall, population genetic analysis supports the possibility that the FCT region gives rise to surface proteins that are largely necessary, but not always sufficient, to confer tissue site preference for infection.

Evolution, Molecular↗

PubMed2006

Role of streptococcal T antigens in superficial skin infection.

FCT region genes of Streptococcus pyogenes encode surface proteins that include fibronectin- and collagen-binding proteins and the serological markers known as T antigens, some of which give rise to pilus-like appendages. It remains to be established whether FCT region surface proteins contribute to virulence by in vivo models of infection. In this study, a highly sensitive and ecologically relevant humanized mouse model was used to measure superficial skin infection. Three genes encoding FCT region surface proteins essential for T-serotype specificity were inactivated. Both the Deltacpa and DeltaprtF2 mutants were highly attenuated for virulence when topically applied to the skin following exponential growth but were fully virulent when delivered in stationary phase. In contrast, the DeltafctA mutant was virulent at the skin, regardless of its initial growth state. Immunoblots of cell extracts revealed anti-FctA-reactive, ladder-like polymers characteristic of streptococcal pili. In addition, FctA formed a heteropolymer with the putative collagen-binding protein Cpa. The DeltafctA mutant showed a loss in anti-Cpa-reactive polymers, whereas anti-FctA-reactive polymers were reduced in the Deltacpa mutant. The findings suggest that both FctA and Cpa are required for pilus formation, but importantly, an intact pilus is not essential for Cpa-mediated virulence. Although it is an integral part of the T-antigen complex, the fibronectin-binding protein PrtF2 is not covalently linked to the FctA- and Cpa-containing heteropolymer derived from cell extracts. The data provide direct evidence that streptococcal T antigens function as virulence factors in vivo, but they also reveal that a pilus-like structure is not essential for the most common form of streptococcal skin disease.

Animals↗

PubMed2005

Specification of the direction of adhesive signaling by the integrin beta cytoplasmic domain.

Integrin adhesion receptors can signal in two directions: first, they can regulate cellular behaviors by modulating cellular signaling enzymes ("outside-in signaling"); second, cells can regulate the affinity of integrins ("inside-out signaling") by such pathways. Integrin beta cytoplasmic domains (tails) mediate both types of signaling, and Src family kinases (SFKs) and talin, which bind to beta tails, are important for integrin signaling. Here, we utilized "homology scanning" mutagenesis to identify beta tail mutants selectively defective in c-Src binding and found that amino acid exchanges affecting a combination of an Arg and Thr residue in the integrin beta3 tail control the binding specificity for SFKs but have no effect on talin binding. Using beta tail mutants at these residues, we found that SFK binding to integrin beta tails is dispensable for inside-out signaling but is obligatory for cell spreading, a marker of outside-in signaling. Conversely, we found that point mutations that disrupt talin binding abolish integrin activation, but they do not inhibit SFK binding to the beta3 tail or the initiation of outside-in signaling once the integrins are in a high affinity form. Thus, we show that inside-out and outside-in integrin signaling are mediated by distinct and separable interactions of the integrin beta tails. Furthermore, based on our results, it is possible to discern the relative contributions of the direction of integrin signaling on biological functions in cell culture and, ultimately, in vivo.

Amino Acid Sequence↗

PubMed2005

Structural diversity of streptokinase and activation of human plasminogen.

The beta domain of streptokinase is required for plasminogen activation and contains a region of sequence diversity associated with infection and disease in group A streptococci. We report that mutagenesis of this polymorphic region does not alter plasminogen activation, which suggests an alternative function for this molecular motif in streptococcal disease.

Amino Acid Sequence↗

PubMed2003

Natural phospholipase A(2) myotoxin inhibitor proteins from snakes, mammals and plants.

A renewed interest in the phenomenon of inter- and intra-species resistance towards the toxicity of snake venoms, coupled with the search for new strategies for treatment of snake envenomations, has prompted the discovery of proteins which neutralize the major toxic components of these venoms. Among these emerging groups of proteins are inhibitors of toxic phospholipases A2 (PLA2s), many of which exhibit a wide range of toxic effects including muscle-tissue damage, neurotoxicity, and inflammation. These proteins have been isolated from both venomous and non-venomous snakes, mammals, and most recently from medicinal plant extracts. The snake blood-derived inhibitors have been grouped into three major classes, alpha, beta, and gamma, based on common structural motifs found in other proteins with diverse physiological properties. In mammals, DM64, an anti-myotoxic protein isolated from opossum serum, belongs to the immunoglobulin super gene family and is homologous to human alpha1B-glycoprotein and DM43, a metalloproteinase inhibitor from the same organism. In plants, a short note is made of WSG, a newly described anti-toxic-PLA2 glycoprotein isolated from Withania somnifera (Ashwaganda), a medicinal plant whose aqueous extracts neutralize the PLA2 activity of the Naja naja venom. The implications of these new groups of PLA2 toxin inhibitors in the context of our current understanding of snake biology as well as in the development of novel therapeutic reagents in the treatment of snake envenomations worldwide are discussed.

Animals↗

PubMed2003

Src kinase activation by direct interaction with the integrin beta cytoplasmic domain.

Src tyrosine kinases transmit integrin-dependent signals pivotal for cell movement and proliferation. Here, we establish a mechanism for Src activation by integrins. c-Src is shown to bind constitutively and selectively to beta3 integrins through an interaction involving the c-Src SH3 domain and the carboxyl-terminal region of the beta3 cytoplasmic tail. Clustering of beta3 integrins in vivo activates c-Src and induces phosphorylation of Tyr-418 in the c-Src activation loop, a reaction essential for adhesion-dependent phosphorylation of Syk, a c-Src substrate. Unlike c-Src, Hck, Lyn, and c-Yes bind more generally to beta1A, beta2, and beta3 cytoplasmic tails. These results invoke a model whereby Src is primed for activation by direct interaction with an integrin beta tail, and integrin clustering stabilizes activated Src by inducing intermolecular autophosphorylation. The data provide a paradigm for integrin regulation of Src and a molecular basis for the similar functional defects of osteoclasts or platelets from mice lacking beta3 integrins or c-Src.

Amino Acid Sequence↗

PubMed2002

Effect of preservatives on IgG aggregation, complement-activating effect and hypotensive activity of horse polyvalent antivenom used in snakebite envenomation.

Intravenous administration of antivenoms is associated with early adverse reactions in a number of cases, but the causes of this phenomenon are still unclear. The effect of preservatives (phenol and thimerosal) on IgG aggregate and dimer formation, in vitro complement-activating effect and hypotensive activity of a whole IgG horse liquid polyvalent antivenom, produced by caprylic acid fractionation, was assessed. These parameters were studied since they have been associated with the development of early adverse reactions to the administration of antivenoms and human immunoglobulins. After a three-year storage period at 4 degrees C, antivenoms with preservatives had an increased content of IgG aggregates and dimers when compared with antivenom devoid of phenol and thimerosal. These observations correlate with a slight increment in the turbidity of preservative-containing antivenoms. The three antivenoms studied (formulation: no preservatives; with phenol and thimerosal; with thimerosal alone) activated human complement in vitro, with only minor quantitative differences among them. When antivenoms were administered as a bolus intravenous injection in rats, a rapid and prominent hypotension of short duration was observed after injection of phenol-containing antivenom, whereas such an effect was absent in antivenom free of preservative and in the one containing only thimerosal. Bolus injection of saline solution with phenol resulted in a similar hypotension, indicating that the effect is due to phenol. However, when phenol-containing antivenom was diluted 1:5 with saline solution before infusion, as occurs in the clinical use of this product, no hypotension was observed. Our results stress the need to evaluate the effects of preservatives on the physicochemical and pharmacological characteristics of antivenoms.

Animals↗