Structural studies on a non-toxic homologue of type II RIPs from bitter gourd: Molecular basis of non-toxicity, conformational selection and glycan structure.

The structures of nine independent crystals of bitter gourd seed lectin (BGSL), a non-toxic homologue of type II RIPs, and its sugar complexes have been determined. The four-chain, two-fold symmetric, protein is made up of two identical two-chain modules, each consisting of a catalytic chain and a lectin chain, connected by a disulphide bridge. The lectin chain is made up of two domains. Each domain carries a carbohydrate binding site in type II RIPs of known structure. BGSL has a sugar binding site only on one domain, thus impairing its interaction at the cell surface. The adenine binding site in the catalytic chain is defective. Thus, defects in sugar binding as well as adenine binding appear to contribute to the non-toxicity of the lectin. The plasticity of the molecule is mainly caused by the presence of two possible well defined conformations of a surface loop in the lectin chain. One of them is chosen in the sugar complexes, in a case of conformational selection, as the chosen conformation facilitates an additional interaction with the sugar, involving an arginyl residue in the loop. The N-glycosylation of the lectin involves a plant-specific glycan while that in toxic type II RIPs of known structure involves a glycan which is animal as well as plant specific.

Relação proteína: carboidrato no desempenho e no metabolismo de híbridos de Pseudoplatystoma fasciatum (fêmea) X Leiarius marmoratus (macho) / Evaluation of protein: carbohydrate ratio in the diet of hybrids of Pseudoplatystoma fasciatum (female) X Leiarius marmoratus (male)

Objetivou-se, neste trabalho, determinar a melhor relação entre proteína e carboidrato na dieta do híbrido carnívoro Pseudoplatystoma fasciatum e Leiarius marmoratus. Utilizou-se um sistema fechado de recirculação de água, composto de 12 caixas de 500L e biofiltro. Foram utilizados 144 juvenis (12/caixa) com peso médio inicial de 12,63±2,52g e comprimento total de 12,34±2,06cm durante 50 dias. Os peixes receberam quatro dietas contendo diferentes relações proteína:carboidrato (1,24; 0,84; 0,56 e 0,33). A relação proteína:carboidrato influenciou o desempenho e os parâmetros metabólicos dos animais. A melhor relação proteína:carboidrato para o desempenho foi 0,84. Os resultados metabólicos demonstraram mobilização de nutrientes para manutenção de glicemia e do crescimento. A relação proteína:carboidrato de 0,84 foi a mais indicada para o híbrido...

The purpose of this study was to determine the best protein:carbohydrate ratio in this hybrid's diet. A water recirculation closed system was used, composed of twelve tanks with 500L each. 144 juveniles (12/tank) with initial weight of 12.63±2.52g and total length of 12.34±2.06cm were distributed. The experiment lasted for 50 days and the fingerlings were feed four diets containing different protein:carbohydrate ratios (1.24; 0.84; 0.56 and 0.33). The protein:carbohydrate ratio influenced performance. The 0.84 ratio promoted better weight gain, smaller apparent feed conversion, great feed intake and largest daily specific growth rate. In short, the 0.84 protein:carbohydrate ratio is most indicated for this hybrid. The results demonstrated metabolic mobilization of nutrients for maintenance of glucose and growth. The 0.84 protein: carbohydrate ratio was recommended for the hybrid...

Computer modelling studies on the modes of binding of some of the α- glycosidically linked disaccharides to concanavalin A.

The possible modes of binding of kojibiose, nigerose, maltose and ManPα(1 →2)Man to concanavalin A have been investigated using computer modelling studies. While α12 linked disaccharides bind to concanavalin A in two modes, i.e. by placing the reducing as well as non-reducing sugar units in the sugar binding site, nigerose or maltose can bind only in one mode, i.e. by placing the non-reducing sugar unit in the binding site. Though, both the sugar residues in α 12 linked disaccharides can reach the binding site, the preference is high for the non-reducing unit. When the non-reducing residue, in any of these disaccharides, enters the binding site, the allowed orientations and the possible hydrogen bonds with the protein seem to be independent of the glycosidic linkage. However, the number of hydrogen bonds the outward sugar residue forms with the protein are dependent on the type of linkage. Atleast one of the hydroxyl groups adjacent to the glycosidic linkage on the outward sugar residue is involved in the formation of a hydrogen bond with the protein suggesting the presence of an extended binding site. The orientation of the reducing sugar residue in the extended binding site is dependent on the linkage. Its orientation in nigerose is flipped when compared to that found in kojibiose or maltose leading to different non-covalent interactions with the protein which affect their binding affinities.