Perforated Bicontinuous Cubic Phases with pH‐Responsive Topological Channel Interconnectivity

Abstract

Lipidic lyotropic liquid crystals are at the frontline of current research for release of target therapeutic molecules due to their unique structural complexity and the possibility of engineering stimuli-triggered release of both hydrophilic and hydrophobic molecules. One of the most suitable lipidic mesophases for the encapsulation and delivery of drugs is the reversed double diamond bicontinuous cubic phase, in which two distinct and parallel networks of ∼4 nm water channels percolate independently through the lipid bilayers, following a Pn3m space group symmetry. In the unperturbed Pn3m structure, the two sets of channels act as autonomous and non-communicating 3D transport pathways. Here, a novel type of bicontinuous cubic phase is introduced, where the presence of OmpF membrane proteins at the bilayers provides unique topological interconnectivities among the two distinct sets of water channels, enabling molecular active gating among them. By a combination of small-angle X-ray scattering, release and ion conductivity experiments, it is shown that, without altering the Pn3m space group symmetry or the water channel diameter, the newly designed perforated bicontinuous cubic phase attains transport properties well beyond those of the standard mesophase, allowing faster, sustained release of bioactive target molecules. By further exploiting the pH-mediated pore-closing response mechanism of the double amino acid half-ring architecture in the membrane protein, the pores of the perforated mesophase can be opened and closed with a pH trigger, enabling a fine modulation of the transport properties by only moderate changes in pH, which could open unexplored opportunities in the targeted delivery of bioactive compounds.

A macroscopic H + and Cl − ions pump via reconstitution of EcClC membrane proteins in lipidic cubic mesophases

“…Voltage of 50 mV was applied to the setup with negative pole on the donor chamber; 1 μg/mL Valinomycin was dissolved in both chambers' solutions. the functionality of membrane proteins reconstituted in lipid mesophases (14). Indeed, although the in meso reconstituted OmpF allows nonselective diffusion of neutral species up to a certain size solely based on concentration gradients between the two chambers, which provide the necessary osmotic stress, in the present system the transport of charge-carrying specific ions has to be rationalized in terms of electrochemical potential and PoissonBoltzmann physics: without a bias potential between the feeding and receiving chamber, any transient charge separation would generate an electric field rapidly hindering further diffusion of charges, preventing the observation of changes in the steady-state stationary transport of Cl − .…”

“…Zabara et al (14,15) have developed a unique method to study the correct reconstitution of membrane proteins in any type of mesophase that can coexist with excess water. In a first study (14), OmpF porin was correctly reconstituted in the bilayers of a Pn3m bicontinuous cubic phase, providing for the first time topological interconnectivities among the two distinct sets of aqueous channels and enabling pH-controlled molecular gating between them.…”

“…In a first study (14), OmpF porin was correctly reconstituted in the bilayers of a Pn3m bicontinuous cubic phase, providing for the first time topological interconnectivities among the two distinct sets of aqueous channels and enabling pH-controlled molecular gating between them. In a following work (15), the same concept was applied to hexagonal mesophases, where again the OmpF membrane protein was correctly reconstituted within the lipid bilayer, improving the transport properties of the mesophase.…”

“…Although the concept introduced by Zabara et al (14,15) is an important proof of concept, the use of membrane proteins enabling only size-selective, passive transport, such as the OmpF porin, limits considerably the potential of the method in targeted drug delivery Significance Membrane protein crystallization from lipidic cubic mesophases has recently revolutionized membrane structural biology, yielding several high-resolution X-ray structures over the past 2 decades. Reconstituted membrane proteins within lipidic cubic mesophases also play a decisive role in other areas of biology, nanotechnology, and drug delivery.…”

Dynamics of different steps of the photopyrolytic cycle of an eminent anticancer drug topotecan inside biocompatible lyotropic liquid crystalline systems

“…[1][2][3][4][5][6][7] Lipid based 'so' and 'wet' lyotropic liquid crystalline (LLC) materials are recognized as the 'smart materials' owing to their remarkable topology, [8][9][10] stimuli responsive phase change 11,12 and multitude of applications in the biological, 5,13 materials 1-7 and pharmaceutical 14,15 elds. These materials can be synthesized by the binary mixture of an amphiphilic surfactant (especially lipid) and water.…”