Characterization of Rat Caltriin Structure and its interactions with model membranes at the air-water interface using molecular dynamics simulations and other bioinformatics tools

CARLOS CORONEL; CARLA MARIANA ROSETTI; EMILIANO A SOTILLE; PERILLO MARIA ANGELICA; ERNESTO JAVIER GRASSO

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Rat caltrin (calcium transport inhibitor), the small and basic protein of theseminal plasma, binds to the spermatozoa during ejaculation and inhibits spermextracellular Ca 2+ uptake. Thus, it prevents the sperm spontaneous acrosomalexocytosis along the female reproductive tract. Although the sequence andsome biological features of rat caltrin were studied, its physicochemicalproperties and 3D structure are still unknown. In this work we predicted the ratcaltrin 3D structure, by molecular homology modeling and threading, whichmaintained its secondary and tertiary structures along molecular dynamicssimulations. The molecular structure was further characterized by circulardichroism. Surface electrostatic potentials and electric fields were calculatedusing the Poisson-Boltzmann equation and the overall protein dipole was alsoevaluated. Bioinformatics tools and available web servers were used to deeplyanalyze physicochemical characteristics such as Kyte and Doolittle Hydropathyscore, solvent accessibility, Wimley-White whole-residue hydrophobicity andhelical wheel projections. The equilibrium spreading pressure was estimated byGibbs adsorption isotherms. Interactions between rat caltrin and phospholipidsmodel membranes were defined by penetration (cut off) studies. Rat caltrin wasable to penetrate into the membranes, mainly in negatively charged surfacesand expanded lateral phase states, and the amino acid residues involved in theprotein-membrane interaction were also predicted. To further characterize theprotein binding to membrane surfaces we carried out simulations in thepresence of negatively charged bilayers. Results presented have significantrelevance to understanding the molecular mechanisms of caltrin to modulatephysiological processes associated with fertilization.