Streptococcal mitogenic exotoxin, SmeZ, is the most susceptible M1T1 streptococcal superantigen to degradation by the streptococcal cysteine protease, SpeB

Superantigens (SAgs) play an important role in the pathogenesis of severe invasive infections caused by Group A Streptococcus (GAS). We had shown earlier that the expression of streptococcal cysteine protease SpeB results in partial loss of the immune-stimulating activity of the native secreted GAS SAgs, namely the streptococcal pyrogenic exotoxins produced by the globally disseminated M1T1 GAS strain, associated with invasive infections worldwide. In this study, we examined the susceptibility of each of the M1T1 recombinant SAgs to degradation by rSpeB. Whereas SmeZ was degraded completely within 30 min of incubation with rSpeB, SpeG, and SpeA were more resistant and SpeJ was completely unaffected by the proteolytic effects of this protease. Proteomic analyses demonstrated that the order of susceptibility of the M1T1 SAgs to SpeB proteolysis is unaltered when they are present in a mixture that reflects their native physiological status. As expected, the degradation of SmeZ abolished its immune stimulatory activity. In silico sequence disorder and structural analyses revealed that SmeZ, unlike the three other structurally related SAgs, possesses a putative SpeB cleavage site within an area of the protein likely to be exposed to the surface. The study provides evidence for the effect of subtle structural differences between highly similar SAgs on their biological activity.     

Multiple noggins in vertebrate genome: cloning and expression of noggin2 and noggin4 in Xenopus laevis

Noggin is a neural inducer secreted by cells of the Spemann organizer. A single noggin gene was identified until very recently in all tested vertebrates. The only exception was zebrafish, in which two close homologs of noggin, named noggin1 and noggin3, and one gene more diverged from them, noggin2, were cloned. Nevertheless, finding of three zebrafish noggins was attributed exclusively to specific genomic duplications in the fish evolutionary branch. However, very recently it was shown that Xenopus tropicalis have additional noggin homolog, called noggin2 [Fletcher, R.B., Watson, A.L., Harland, R.M. (2004). Expression of Xenopus tropicalis noggin1 and noggin2 in early development: two noggin genes in a tetrapod. Gene Expr. Patterns 5, 225-230], which indicates at least two independent noggin genes in vertebrate phylum. Now we report identification of two novel noggin homologs in each of so evolutionary distant species as Xenopus laevis, chicken and fugu. One of these noggins is ortholog of the X. tropicalis and zebrafish noggin2, whereas another, named noggin4, was not known previously. In the X. laevis embryos, the expression of noggin2 very resembles that of its counterpart in X. tropicalis: it begins with neurulation at the anterior margin of the neural plate and, afterward, continues mainly in the forebrain and dorsal hindbrain. At the same time, noggin4 is expressed starting from the beginning of gastrulation, throughout the ectoderm, with a local expression maximum in the prospective anterior neurectoderm. Later, it is widely expressed on the dorsal side of embryo, including neural tube, eyes, otic vesicles, cranial placodes, branchial arches, and somites. The data presented here demonstrate that the vertebrate phylum contains at least three distinct noggin genes.     

The Cytoskeletal Protein Zyxin Modulates the Expression of the Target Genes of the Shh Signaling Cascade in the Cells of the Neural Plate of Embryos of the Spur-Toed Frog Xenopus laevis

Russian Journal of Bioorganic Chemistry - It has been shown earlier in a study of the role of the cytoskeletal protein zyxin in cell differentiation in the primordium of the central nervous system...     

Interaction of secreted factor Agr2 with its potential receptors from the family of three-finger proteins

Interactions of the secreted protein XAgr2 of the Agr (anterior gradient proteins) family with six submembrane proteins, Tfp1–6, from the family of three-finger proteins Ly6 were studied in Xenopus laevis embryos. Earlier, other authors have shown that the newt homologue of XAgr2 is able to bind the Prod1 three-finger protein, which participates in the establishment of the proximal-to-distal pattern of cell differentiation in the regenerating blastema of a newt’s limb bud. Here, we identified six homologues of Prod1 in Xenopus laevis genome named Tfp1–6. By co-immunoprecipitation, we demonstrated that among these homologues, Tfp4 is the most probable receptor of XAgr2. Further study of the revealed interactions between XAgr2 and Tfp4 is of significant interest because XAgr2 is involved in the signaling pathways that regulate neural system development and the body appendages regeneration.     

Analysis of foreign epitope inserts in HBcAg. Approaches to solving the problem of core particle self-assembly

The hepatitis B virus core antigen (HBcAg) is a promising protein carrier for exposing the epitopes of various human and animal pathogens. HBcAg-based chimeric proteins can be used in creating highly efficient vaccines; however, not all chimeric HBcAg with foreign epitope inserts are capable of assembly into virus-like particles. Using computer programs ProAnalyst, SALIX, and QSARPro, we examined the relationship between the self-assembly capability of chimeric HBcAg and the physicochemical properties of the inserts. The self-assembly was found to be impaired when the inserted peptides contained highly hydrophobic and bulky residues tending to form β-structures; this especially concerned the C-proximal residues in the insert. Recommendations were elaborated for constructing foreign epitopes that would ensure correct self-assembly of chimeric HBcAg particles.