Features | Partner Sites | Information | LinkXpress
Sign In
GLOBETECH PUBLISHING LLC
GLOBETECH PUBLISHING LLC
GLOBETECH MEDIA

pH-Dependence Described for Key Membrane Bilayer Properties

By BiotechDaily International staff writers
Posted on 16 Oct 2013
Image: pH-dependent changes in intermolecular packing and symmetry of bilayer tails (Photo courtesy of Northwestern University).
Image: pH-dependent changes in intermolecular packing and symmetry of bilayer tails (Photo courtesy of Northwestern University).
Scientists have discovered specific pH-dependent changes in structural symmetry and density of bilayer membranes, enabling a new venue for controlled alteration of properties important for advancement of cell biology and biotechnology.

The study, an interdisciplinary collaboration between multiple Northwestern University laboratories led by principal investigators of Northwestern’s McCormick School of Engineering and Applied Science (Evanston, IL, USA), showed how crystalline order within bilayer membranes, formed from coassembled cationic- and anionic-head amphiphile molecules, can be controlled by varying pH and molecular hydrophobic-tail length. “In nature, living things function at a delicate balance: acidity, temperature, all its surroundings must be within specific limits, or they die,” said Prof. Monica Olvera de la Cruz of Northwestern’s McCormick School of Engineering; “When living things can adapt, however, they are more functional. We wanted to find the specific set of conditions under which bilayers, which control so much of the cell, can morph in nature.”

In bilayer membranes, the two layers of amphiphile molecules form a crystalline shell around its contents. The density and arrangement of the molecules determine the membrane’s porosity, strength, and other properties. Taking advantage of the ionizable charge in the head groups, the team coassembled dilysine (+2) and carboxylate (-1) amphiphile molecules of varying hydrophobic-tail lengths into bilayer membranes at various (physiologically relevant) pH levels, which changed the effective charge of the heads. Then, using X-ray scattering technology at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) at Argonne National Laboratory’s Advanced Photon Source, the researchers analyzed the resulting crystallization formed by the bilayer molecules. Freezing has generally been used to produce electron microscope images of membrane structures, however this process is labor-intensive and changes the structural fidelity, making it less relevant for understanding membrane assembly and behavior under physiological conditions.

From the results, the researchers found that most molecules did not notably respond to the change in acidity, but for those that possessed a critical tail length (which correlates to the level of hydrophylia) the charge of the heads changed to the extent that their two-dimensional crystallization morphed from a periodic rectangular-patterned lattice in more basic pH solutions to a hexagonal lattice in more acidic pH solutions. Shells with a higher symmetry (e.g., hexagonal) are stronger and less brittle than those with lesser symmetry. The change in pH also altered bilayer thickness and compactness. Changing the crystallinity, density, and spacing of molecules within membranes could help researchers control diffusion rates and the encapsulation and release efficiency of molecules in vesicles, which would further shed light on cell function and could enable advances in drug delivery and other bio-inspired technology.

The study was published ahead of print online September 24, 2013, in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Related Links:
McCormick School of Engineering and Applied Science at Northwestern University



Channels

Genomics/Proteomics

view channel
Image: The photo shows a mouse pancreatic islet as seen by light microscopy. Beta cells can be recognized by the green insulin staining. Glucagon is labeled in red and the nuclei in blue (Photo courtesy of Wikimedia Commons).

Regenerative Potential Is a Trait of Mature Tissues, Not an Innate Feature of Newly Born Cells

Diabetes researchers have found that the ability of insulin-producing beta cells to replicate and respond to elevated glucose concentrations is absent in very young animals and does not appear until after weaning.... Read more

Drug Discovery

view channel
Image: Wafers like the one shown here are used to create “organ-on-a-chip” devices to model human tissue (Photo courtesy of Dr. Anurag Mathur, University of California, Berkeley).

Human Heart-on-a-Chip Cultures May Replace Animal Models for Drug Development and Safety Screening

Human heart cells growing in an easily monitored silicon chip culture system may one day replace animal-based model systems for drug development and safety screening. Drug discovery and development... Read more

Business

view channel

Roche Acquires Signature Diagnostics to Advance Translational Research

Roche (Basel, Switzerland) will advance translational research for next generation sequencing (NGS) diagnostics by leveraging the unique expertise of Signature Diagnostics AG (Potsdam, Germany) in biobanks and development of novel NGS diagnostic assays. Signature Diagnostics is a privately held translational oncology... Read more
 
Copyright © 2000-2015 Globetech Media. All rights reserved.