Crystallization and biochemical characterization of an archaeal lectin from Methanococcus voltae A3.

A lectin from Methanococcus voltae A3 has been cloned, expressed, purified and characterized. The lectin appears to be specific for complex sugars. The protein crystallized in a tetragonal space group, with around 16 subunits in the asymmetric unit. Sequence comparisons indicate the lectin to have a ß-prism I fold, with poor homology to lectins of known three-dimensional structure.

Distortion of the ligand molecule as a strategy for modulating binding affinity: Further studies involving complexes of jacalin with ß-substituted disaccharides.

Crystal structures of jacalin in complex with GlcNAc ß-(1,3) Gal-ß-OMe and Gal ß-(1,3) Gal-ß-OMe have been determined. The binding of the ligands to jacalin is similar to that of analogous α-substituted disaccharides. However, the ß-substituted ß-(1,3) linked disaccharides get distorted at the anomeric center and the glycosidic linkage. The distortion results in higher internal energies of the ligands leading to lower affinity to the lectin. This confirms the possibility of using ligand distortion as a strategy for modulating binding affinity. Unlike in the case of ß-substituted monosaccharides bound to jacalin, where a larger distortion at the anomeric center was observed, smaller distortions are distributed among two centers in the structures of the two ß-substituted ß-(1,3) linked disaccharides presented here. These disaccharides, like the unsubstituted and α-substituted counterparts, bind jacalin with the reducing Gal at the primary binding site, indicating that the lower binding affinity of ß-substituted disaccharides is not enough to overcome the intrinsic propensity of Gal ß-(1,3) Gal-based disaccharides to bind jacalin with the reducing sugar at the primary site. © 2017 IUBMB Life, 69(2):72-78, 2017.

Effect of linkage on the location of reducing and nonreducing sugars bound to jacalin.

The crystal structures of jacalin complexed with Gal α-(1,4) Gal and Gal α-(1,3) Gal ß-(1,4) Gal have been determined with the primary objective of exploring the effect of linkage on the location of reducing and non-reducing sugars in the extended binding site of the lectin, an issue which has not been studied thoroughly. Contrary to the earlier surmise based on simple steric considerations, the two structures demonstrate that α-linked sugars can bind to jacalin with nonreducing sugar at the primary binding site. This is made possible substantially on account of the hitherto underestimated plasticity of a non-polar region of the extended binding site. Modeling studies involving conformational search and energy minimization, along with available crystallographic and thermodynamic data, indicate a strong preference for complexation with Gal ß-(1,3) Gal with the reducing Gal at the primary site, followed by that with Gal α-(1,3) Gal, with the reducing or non-reducing Gal located at the primary binding site. This observation is in consonance with the facility of jacalin to bind mucin type O-glycans containing T-antigen core. © 2016 IUBMB Life, 68(12):971-979, 2016.

Jacalin-carbohydrate interactions: distortion of the ligand molecule as a determinant of affinity.

Jacalin is among the most thoroughly studied lectins. Its carbohydrate-binding site has also been well characterized. It has been postulated that the lower affinity of ß-galactosides for jacalin compared with α-galactosides is caused by steric interactions of the substituents in the former with the protein. This issue has been explored energetically and structurally using different appropriate carbohydrate complexes of jacalin. It turns out that the earlier postulation is not correct. The interactions of the substituent with the binding site remain essentially the same irrespective of the anomeric nature of the substitution. This is achieved through a distortion of the sugar ring in ß-galactosides. The difference in energy, and therefore in affinity, is caused by a distortion of the sugar ring in ß-galactosides. The elucidation of this unprecedented distortion of the ligand as a strategy for modulating affinity is of general interest. The crystal structures also provide a rationale for the relative affinities of the different carbohydrate ligands for jacalin.

Associação entre ângulo de fase, PRISM I e gravidade da sepse / Association between phase angle, PRISM I and sepsis severity

JUSTIFICATIVA E OBJETIVOS: Ângulo de fase (AF) é a diferença entre a voltagem e a corrente e pode ser usado como indicador de massa celular corporal. Estudos clínicos mostram que baixos AF estão associados com morbidade e mortalidade em pacientes críticos. O objetivo deste estudo foi conhecer a relação entre AF e o escore pediátrico de risco de mortalidade (PRISM I) em pacientes pediátricos sépticos críticos, associando esse indicador c om a gravidade da sepse. MÉTODO: Estudo transversal realizado na Unidade de Terapia Intensiva (UTI) Pediátrica do Instituto Fernandes Figueira. Os pacientes foram caracterizados de acordo com faixa etária, sexo, gravidade da sepse, etiologia da insuficiência respiratória, escore de PRISM I, grau de disfunção de múltiplos órgãos e sistemas (DMOS). A análise de bioimpedância elétrica (BIA) foi realizada em todos os pacientes e, através da razão dos valores de reactância (Xc) e resistência (R), foi calculado o AF (AF = arco-tangente da reactância/resistência x 180º /Pi). RESULTADOS: Foram avaliados 75 pacientes, sendo 68 (90,7 por cento) com sepse. A incidência de choque séptico foi 39,7 por cento, sepse grave 42,6 por cento e sepse 17,6 por cento. Não houve diferença estatística significativa entre as médias de ângulo de fase e as categorias de PRISM I, porém observou-se uma relação inversa entre os valores de AF e as categorias de PRISM I, DMOS e tempo de internação. Os valores mais baixos de AF (1,5º-2,2º) foram observados no maior escore de PRISM I (> 30 por cento). CONCLUSÕES: Os pacientes pediátricos críticos apresentaram baixos valores de angulo de fase, portanto deve ter a sua importância prognóstica estudada.

BACKGROUND AND OBJECTIVES: Phase angle (PA) is the difference between voltage and current and can be used as an indicator of body cell mass. Clinical studies show that low phase angle is associated with morbidity and mortality of critical patients. The purpose of this study was to know the relation between phase angle and the Pediatric Risk of Mortality I (PRISM I) score, associating this score with the severity of sepsis. METHODS: A transversal study was performed at the Pediatric Intensive Care Unit (PICU) in Instituto Fernandes Figueira. The patients were classified according to age, gender, sepsis severity, cause of respiratory failure, PRISM I score, multiple organ dysfunction syndromes (MODS). Electrical bioimpedance analysis (BIA) was performed in all patients. Phase angle was calculated directly from reactance (Xc) and resistance (R). AF = arc-tangent reactance/resistance x 180º/Pi. RESULTS: 75 patients (68 septic) were evaluated. The incidence of septic shock was 39.7 percent, severe sepsis 42.6 percent and sepsis 17.6 percent. There was no significative statistical difference between the mean values of BIA and the categories of PRISM I, MODS, or the length of stay the PICU. The PA's lowest values (1.5º-2.2º) were associated to the greatest PRISM's scores (> 30 percent). CONCLUSIONS: Pediatric critical patients show low phase angle values, which might have prognostic implication.