(462e) Optimization-Based Computational Tools for Precise Engineering of Channel Proteins and Organic Cages to Perform Angstrom-Scale Separations

Monodispersed angstrom-size pores embedded in a suitable matrix are promising for highly selective membrane-based separations. They can provide substantial energy savings in water treatment and small molecule bioseparations. Such membrane proteins (primarily aquaporins) are commonplace in biological membranes but difficult to implement in synthetic industrial membranes due to their modest and non-tunable selectivity. Here we describe PoreDesigner, a computational design workflow for the redesign of the robust beta-barrel Outer Membrane Protein F as a scaffold targeting of any specified pore diameter (spanning 3–10 Å), internal geometry and chemistry. PoreDesigner uses a mixed-integer linear program to optimally place long side -chain hydrophobic amino acids at the pore constriction region that yield a smaller and more hydrophobic pore by maximizing the interaction energy between the pore wall and the permeating water wire. We appended a design assessment step in each iteration by accepting only those designs that fit the user-fed pore dimensions. We first ran PoreDesigner to obtain pore sizes lesser than 4 Šthat would exhibit aquaporin-like single file water transport yet maintaining high water permeation rates. 40 accepted OmpF redesigns were obtained and were classified as off-center (OCD), uniform closure (UCD), and cork-screw designs (CSD) dictated by their internal pore architecture. The narrowest pore design from each category was chosen and set in a membrane-patch and an all-atom 200ns molecular dynamics forward-osmosis simulation was performed to corroborate the PoreDesigner-predicted pore sizes. Subsequently, stopped-flow light scattering experiments on these three designs revealed complete salt rejection by the UCD mutant and an order of magnitude higher single-channel water permeabilities than any reported aquaporin till date (for all three designs). Follow-up efforts are being made to tune the membrane-pore interactions for various biomimetic membrane materials, by systematic alteration of the hydrophobicity of the membrane-facing residues without altering their pore size. This would enable easier incorporation of these redesigned proteins in 2D planar membrane sheets and serve as viable filtration assemblies for performing precise angstrom-scale separations. PoreDesigner has been made freely downloadable from http://www.maranasgroup.com/software.htm. Additionally, a similar computational architecture has been used to design complex organic cage-like molecules and their various oligomeric states have been explored to yield gyroid single-file water transport networks. These when incorporated in biomimetic membrane assemblies have been experimentally seen to result in extremely effective membrane materials that allow high water permeation rates without leaking any ions whatsoever.