| Abstract
| - Molecular dynamics (MD) simulations have been performed onadipocyte lipid-binding protein,using the apo and holo forms, bound with stearic and oleic acid.The contribution of electrostatics toprotein dynamics and ligand stabilization was assayed by perturbing theelectrostatic charge of Arg106and Arg126 (positive → neutral) and the fatty acid (132H) headgroup(negative → neutral). MD simulationsfor charged holo forms demonstrated significantly greater electrostaticbinding energy and a more stabilizedhydrogen bond network than simulations performed using neutral forms.Electrostatics, however, appearedto have little effect on fatty acid behavior, e.g.,fluctuation of the dihedral head group; number of dihedraltransitions within the acyl chain; and change in the end-to-enddistance for fatty acid. Instead, fatty acidbehavior appeared to be dictated by the presence or absence of anunsaturated bond within the acyl chain.A significantly greater number of transitions were observed duringMD simulations in oleic than stearicacid. In addition, significantly greater fluctuation was observedfor oleic acid, within the C2 headgroupand C9 and C11 dihedrals (which lie adjacent to the olefin bond ofoleic acid). The dynamic behaviorof the acyl chain may thereby be more a property of van der Waalscontact, and the degree of acyl chainunsaturation, than a function of electrostatics. In the absence offatty acid, an increase in distance betweenguanidino carbon centered atoms of Arg126 and Arg106 was observedduring MD simulations of thecharged apo form. This effect not observed with the neutral apoform or in any of the holo complexesand, presumbably, was a result of repulsion between the negativelycharged arginine sidechains. Conservedwaters reflected substantially lower mean-square displacement (msd) inall simulations, except the neutralapo form. This suggests that the presence of either charged aminoacids or lipid provides increased orderfor water within the binding pocket. These results provide adynamic perspective of the interactive naturewithin the FABP binding pocket regulated in a complex manner by theelectrostatics within the bindingcavity, acyl chain structure and behavior, and waterenergetics.
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