Molecular dynamics and circular dichroism studies of human and rat C-peptides.

Proinsulin C-peptide has been recently described as an endogenous peptide hormone, responsible for important physiological functions others than its role in proinsulin processing. Accumulating evidences that C-peptide exerts beneficial effects in the treatment of long term complications of patients with type 1 diabetes mellitus indicate that this molecule may be administered together with insulin in future therapies. Despite its clear pharmacological interest, the secondary and three-dimensional (3D) structures of human C-peptide are still points of controversy. In the present work we report molecular dynamics (MD) simulations of human, rat I and rat II C-peptides. A common experimental strategy applied to all peptides consisted of homology building followed by multinanosecond MD simulations in vacuum and water. Circular dichroism (CD) experiments of each peptide in the absence and presence of 2,2,2-trifluoroethanol (TFE) were performed to support validation of the theoretical models. A multiple sequence alignment of 23 known mammalian C-peptides was constructed to identify significant conserved sites that would be important for the maintenance of secondary and tertiary structures. The analysis of the molecular dynamics trajectories for the human, rat I and rat II molecules have shown quite different general behavior, being the human C-peptide more flexible than the two others. Human and rat C-peptides exhibit very stable turn-like structures at the middle and C-terminal regions, which have been described as potential active sites of C-peptides. Human C-peptide also presented a short alpha-helix throughout the MD, which was not found in the rat molecules. CD data is in very good agreement with the MD results and both methods were able to identify a greater structural stability and potential in rat C-peptides when compared to the human C-peptide. The simulation results are discussed and validated in the light of multiple sequence alignment, recent experimental data from the literature and our own CD experiments.

Detection and characterization of leishmania antigens from an American cutaneous leishmaniasis vaccine for diagnosis of visceral leishmaniasis.

Antigens were isolated from vaccines against American Cutaneous Leishmaniasis (ACL) and their reactivity tested against nine different groups of human sera and two groups of dog sera. These antigens react specifically with human and dog visceral leishmaniasis sera when compared to sera from non-infected individuals. Sera from humans from endemic areas of ACL before, or one year after, vaccination, and ACL patients treated and cured by immunotherapy with polyvalent vaccine, did not display significant differences of reactivity to these antigens. In contrast, they displayed a significantly higher reactivity to the antigens when compared to sera from healthy humans from non-endemic areas. No sera reactivity was observed with patients carrying Chagas' disease or tuberculosis. These antigens are polysaccharides aggregates and present molecular masses ranging from 90 to over 200 KDa. These data suggest the use of these antigens for sero-diagnosis of human and canine visceral leishmaniasis.

Gamma trypsin: purification and physicochemical characterization of a novel bovine trypsin isoform.

A novel bovine trypsin isoform was purified from commercial sample by ion exchange chromatography by Sephadex SP C50®. New isoform contains in addition of loss of N-terminus hexapeptide (as found in parent molecule ß-trypsin) an intra-chain split between Lys-155 and Ser-156. The novel enzyme denominate γ-trypsin showed similar properties with α-trypsin isoform in polypeptide number chain (two chain), molecular masses (23,312 Da), secondary structure, hydrodynamic radius and others. In spite of enzymatic and structural similarities of both isoforms, γ-trypsin preferably has a lower rate formation from ß-trypsin, a lower surface charge, but the γ-trypsin has a higher thermal stability than α-trypsin. Due to obtaining facility of purification of bovine trypsin isoforms from commercial font, and properties described above, this enzyme becomes an interesting alternative for the food industry, detergent and biocatalysis research.

Leishmania major-like antigen for specific and sensitive serodiagnosis of human and canine visceral leishmaniasis.

An antigen (LMS) prepared from Leishmania major-like promastigotes was used in an enzyme-linked immunosorbent assay (ELISA) for the diagnosis of human and dog visceral leishmaniasis. The results were compared with those from the indirect immunofluorescent antibody test (IFAT). A total of 1822 canine sera were tested, including sera from dogs with visceral leishmaniasis, transmissible venereal tumors, ehrlichiosis, rickettsiosis, or Chagas' disease and sera from healthy dogs. The antigen was also tested with 227 samples of human sera, including sera from patients with visceral, cutaneous, or diffuse cutaneous leishmaniasis and from noninfected individuals, as well as sera from patients with Chagas' disease, toxoplasmosis, rickettsiosis, hepatitis B, schistosomiasis, ascaridiasis, malaria, rheumatoid factor, leprosy and rheumatoid factor, tuberculosis, or leprosy. All dogs and all human patients had a clinical and/or serological and/or parasitological diagnosis. For detecting antibodies in sera from dogs with leishmaniasis, the antigen showed a sensitivity of 98%, specificity of 95%, and concordance of 93% and when used for detecting antibodies in human sera presented a sensitivity of 92%, specificity of 100%, and concordance of 92%. Comparison between ELISA and IFAT demonstrated that ELISA using the LMS antigen yielded more reliable results than IFAT. The LMS antigen displayed no cross-reactivity with sera from patients or dogs that had any of the other diseases tested.