Features | Partner Sites | Information | LinkXpress
Sign In
PZ HTL SA
GLOBETECH PUBLISHING LLC
GLOBETECH PUBLISHING LLC

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



comments powered by Disqus

Channels

Genomics/Proteomics

view channel

New Program Encourages Wide Distribution of Genomic Data

A new data sharing program allows genomics researchers and practitioners to analyze, visualize, and share raw sequence data for individual patients or across populations straight from a local browser. The sequencing revolution is providing the raw data required to identify the genetic variants underlying rare diseases... Read more

Drug Discovery

view channel
Image: The nano-cocoon drug delivery system is biocompatible, specifically targets cancer cells, can carry a large drug load, and releases the drugs very quickly once inside the cancer cell. Ligands on the surface of the \"cocoon\" trick cancer cells into consuming it. Enzymes (the “worms\" in this image) inside the cocoon are unleashed once inside the cell, destroying the cocoon and releasing anticancer drugs into the cell (Photo courtesy of Dr. Zhen Gu, North Carolina State University).

Novel Anticancer Drug Delivery System Utilizes DNA-Based Nanocapsules

A novel DNA-based drug delivery system minimizes damage to normal tissues by utilizing the acidic microenvironment inside cancer cells to trigger the directed release of the anticancer drug doxorubicin (DOX).... Read more

Lab Technologies

view channel

Experimental Physicists Find Clues into How Radiotherapy Kills Cancer Cells

A new discovery in experimental physics has implications for a better determination of the process in which radiotherapy destroys cancer cells. Dr. Jason Greenwood from Queen’s University Belfast (Ireland) Center for Plasma Physics collaborated with scientists from Italy and Spain on the work on electrons, and published... Read more

Business

view channel

Interest in Commercial Applications for Proteomics Continues to Grow

Increasing interest in the field of proteomics has led to a series of agreements between private proteomic companies and academic institutions as well as deals between pharmaceutical companies and novel proteomics innovator biotech companies. Proteomics is the study of the structure and function of proteins.... Read more
 
Copyright © 2000-2014 Globetech Media. All rights reserved.