Biophysics Laboratory in NCU/CCS

This lab started the biophysics research in 1995. The goal is to understand the functions of membrane-active bio-molecules, such as anti-microbial peptides, ion-channel proteins and DNA. This lab has set up the world-class experiment of lamellar x-ray diffraction/osmosis (LXDO). The change of bilayer structure with 0.1Å resolution and the lipid area compressibility under high tension are now detectable. Many questions about membrane properties, which have been lasted for a long time, now have the answers because of advanced LXDO: 1. The multi-lamellar bilayers are getting soft to swell more water between them, when cooled down to approach the gel phase transition. 2. Depending on lipid¡¦s hydrocarbon chains branched or not, the structure of lipid¡¦s headgroup in the bilayer could be changed or unchanged upon the temperature and/or the osmotic pressure. 3. There is a threshold above which the osmotic pressure begins to compress the lipid cross section area for gel phase bilayers. 4. The mechanism that the osmotic pressure reduces the membrane surface tension is now clear, from which the correct formula to determine the area compressibility is established.  Currently, this LXDO technique is applied to the study of the quasi-real membranes, made of mulit-component lipids, cholesterol, etc.

In addition to LXDO, this lab has also set up the experiment of oriented circular dichroism (OCD) to measure the protein secondary configuration and its orientation in lipid membranes. Combining LXDO and OCD, this lab has discovered the mechanism of antimicrobial peptides to kill the microbes and bacterium. The antimicrobial peptides, when adsorbed on membrane surfaces, generate a stretch surface tension to make the membrane thinning. As exceeding certain peptide concentration, the peptides are able to form lipid/peptide pores, that is, to punch holes on membranes, apparently a mechanism to kill the microbes and bacterium. Currently, we are investigated the factors that are potentially to control the mechanism. They include: 1. Membrane properties -- the ratio of membrane hydrophobic and hydrophilic area, the membrane thickness, the membrane stretch modulus, the membrane charges; 2. Peptide properties --  the distribution of amino acids, the type and the dimension of secondary configuration, the charges etc.

The future topics we will be interesting in are: 1. Protein folding and its functioning in membrane. 2. DNA coupling with membrane and its functioning. 3. The mechanism that the charged penetrating-peptides bring the big molecules such as protein, enzyme and DNA to cross the membrane into the cell.

10/8, 2002 by Fang-Yu Chen