Molecular basis of the anchoring and stabilization of human islet amyloid polypeptide in lipid hydroperoxidized bilayers.

The molecular structure of membrane lipids is formed by mono- or polyunsaturations on their aliphatic tails that make them susceptible to oxidation, facilitating the incorporation of hydroperoxide (R-OOH) functional groups. Such groups promote changes in both composition and complexity of the membrane significantly modifying its physicochemical properties. Human Langerhans islets amyloid polypeptide (hIAPP) is the main component of amyloid deposits found in the pancreas of patients with type-2 diabetes (T2D). hIAPP in the presence of membranes with oxidized lipid species accelerates the formation of amyloid fibrils or the formation of intermediate oligomeric structures. However, the molecular bases at the initial stage of the anchoring and stabilization of the hIAPP in a hydroperoxidized membrane are not yet well understood. To shed some light on this matter, in this contribution, three bilayer models were modeled: neutral (POPC), anionic (POPS), and oxidized (POPCOOH), and full atom Molecular Dynamics (MD) simulations were performed. Our results show that the POPCOOH bilayer increases the helicity in hIAPP when compared to POPC or POPS bilayer. The modification in the secondary structure covers the residues of the so-called amyloidogenic core of the hIAPP. Overall, the hydroperoxidation of the neutral lipids modifies both the anchoring and the stabilization of the peptide hIAPP by reducing the random conformations of the peptide and increasing of hydrogen bond population with the hydroperoxidized lipids.

Finite-temperature effect in the O-acylation of (R,S)-propranolol catalyzed by Candida antarctica lipase B.

CalB is a triacylglycerol hydrolase (E.C.3.1.1.3) used in the O-acylation of the beta-adrenergic blocking agent (R,S)-propranolol. The catalytic mechanism involves two steps: enzyme acylation and enzyme deacylation. The enantioselectivity of the O-acylation of (R,S)-propranolol originates from the second step, where the acyl-enzyme transfers the acyl group to the racemic substrate. This step occurs via an initial Michaelis complex (MCC) and a tetrahedral intermediate (TI-2). To gain more insight into the molecular basis of this reaction, we performed an exhaustive conformational sampling along the reaction coordinate of the enantioselective step of the reaction (MCC→TI-2→EPC) applying a QM/MM MD protocol (SCC-DFTB/CHARMM) in combination with umbrella sampling and the weighted histogram analysis method. To identify finite temperature effects we compare the PMF and the potential energy pathway. It is found that the effect of the finite temperature in this reaction is a destabilization of the tetrahedral intermediate and an increase of the barrier height of its formation. This increase is higher for the S-enantiomer.

Función de los confórmeros de ataque cercano en la acilación enantioselectiva del (R,S)-propranolol catalizada por lipasa B de Candida antárctica / Rol of the near attack conformers during enantioselective acylation of (R,S)-propranolol catalysed by Candida antarctica lipase B

RESUMEN La lipasa B de Candida antárctica (CalB) se ha utilizado en la acilación quimio- y enantioselectiva del racemato (R,S)-propranolol. CalB tiene enant¡oselect¡v¡dad moderada (£=63) por el R-propranolol. La enantioselectividad, se origina en la reacción de transferencia del grupo acilo desde la serina catalítica, acilada, al propranolol. La fase inicial de esta reacción involucra la formación de complejos de Michaelis y posteriormente conformaciones de ataque cercano. El análisis de las conformaciones de ataque cercano ha permitido en varios casos explicar el origen de la catálisis o reproducir el efecto catalítico. En este trabajo se profundiza en la comprensión la función de las conformaciones de ataque cercano en la enantioselectividad de la acilación del (R,S)-propranolol catalizada por CalB. Para lo anterior se realizó un estudio detallado de los complejos de Michaelis y de las conformaciones de ataque cercano del paso enantioselectivo de la reacción de acilación del (R,S)-propranolol utilizando un protocolo de dinámica molecular QM/MM (SCCDFTB/CHARMM) utilizando 6 distribuciones de velocidades iniciales y simulaciones de 2,5 ns. Se estudiaron 7 complejos CalB-propranolol. Los enlaces de hidrógeno del sitio activo de CalB acilada relevantes para la actividad catalítica fueron estables en todas las simulaciones. Las poblaciones de los complejos de Michaelis y de las conformaciones de ataque cercano son dependientes de la distribución de las velocidades iniciales de la dinámica molecular. La enantioselectividad moderada de CalB acilada, encontrada experimentalmente, puede ser parcialmente atribuida a la alta población de conformaciones de ataque cercano observada para el S-propranolol.

ABSTRACT Candida antarctica lipase B (CalB) has been used for chemo- and enantioselective acylation of racemic (R,S)-propranolol, with moderate enantioselectivity (£=63) for R-propranolol. The enantioselective step in this reaction is the transfer of an acyl group from the catalytic acylated serine to propranolol. The initial phase of this reaction involves the formation of Michaelis complexes, followed by the formation of near-attack complexes. The analysis of the near-attack complexes has in several cases permitted to explain the origin of the catalysis or to reproduce the catalytic effect. The aim of this study was improve the understanding of the role of the near-attack complexes for the enantioselectivity of the acylation of (R,S)-propranolol, catalyzed by CalB. To this purpose a detailed investigation of the Michaelis and near-attack complexes of the enantioselective step of the acylation of (R,S)-propranolol using QM/MM molecular dynamics was performed. Several simulations (each 2,5 ns) with different initial velocity distributions were performed. In total seven CalB-propranolol complexes were studied. The hydrogen bonds in the active site of CalB, which are relevant for the catalytic activity, are stable in all simulations. The lifetime of the Michaelis complexes is considerably shorter than the simulation time. Conclusions: The populations of the Michaelis and near-attack complexes depend on the initial velocity distribution in the molecular dynamics simulations. The experimentally observed moderate enantioselectivity may be partially attributed to the high population of near-attack conformations of S-propranolol.

Diabetes mellitus como factor de riesgo para la disfunción sexual erectil en pacientes de 30 a 60 años de edad del Hospital Universitario de Caracas en el período 1999-2002 / Diabetes mellitus with risk factor for the sexual inpotence in patients of 30 to 60 year of age of Caracas Universitary Hospital in the period 1999-2002

La disfunción sexual eréctil se define como la incapacidad de tener o mantener una erección del pene que sea suficiente para la penetración vaginal y para permitir un acto sexual satisfactorio. Para que esta erección se logre deben interactuar varios factores vasculares, neurológicos y bioquímicos. Las enfermedades que provoquen alteración de estos factores conllevan a la aparición de disfunción eréctil, entre ellas tenemos a la diabetes mellitus, causante de trastornos microvasculares, neurológicos, bioquímicos, hormonales y metabólicos. Existen referencias de que en un 30 por ciento y cincuenta por ciento de los hombres diabéticos desarrollan disfunción sexual, eréctil, tras 10 años de evolución, independientemente del tipo de diabetes que tengan. Se propuso como objetivo determinar la asociación de diabetes mellitusy disfunción sexual eréctil, a través de un estudio prospectivo de casos y controles, demostrándose que la diabetes aumentaba el riesgo de adquirir la disfunción eréctil entre 2,47 y 13,6 veces, con un RR= 5,8, y se le calculó un riesgo atribuible de 0,187, concluyendo que la diabetes mellitus es un fuerte factor de riesgo para el desarrollo de la enfermedad, causante de 18,7 por ciento de los casos de la disfunción eréctil, cifra inferior a los de otros estudios anteriores (30-50 por ciento)