Thursday, 14 July 2011

Membrane proteins

Those proteins embedded in cell membranes make are difficult to study.  A Nobel Prize was given to the first membrane proteins that were crystallized.  So understanding membrane proteins are very important.  You can think of these membrane proteins as being a door and its frame and the walls being the cell membrane holding that door in plane and helping it with its function.  If the membrane is distorted (possibly due to anesthetics, lipid molecules or surfactants) like a warped wall it might stop the door from its primary function of opening and closing.  Biologists, biochemists and biophysicists are always trying to remove the doors from the walls so we can study them.  However, we want to study the door intact with all its hinges, door knob ect. not broken.  How do people do this?

Scientists use some kind of surfactant to first surround the membrane proteins, and extract them.  Many times these membrane proteins are not functional once they are extracted.  In the recent article by Matar-Merheb states that the 'underlying reason is the fact that detergents do not stabilize membrane domains as efficiently as natural lipids in membranes, often leading to a partial to complete loss of activity/stability during protein extraction and purification and preventing crystallization in an active conformation.'  When you cannot find good surfactants to extract proteins you do the next best thing.  You make them.  These French groups in this paper did just that.  They made 'anionic calix arene based detergents (C4Cn, n = 1–12)  designed to structure the membrane domains through hydrophobic interactions and a network of salt bridges with the basic residues.'  They reported that these molecules behave as surfactants and as measured using a Kibron Mictrough xl 'measured from the plots as the intersection between the plateau reached at the minimal value of the surface tension and the tangent of each curve' they obtained 'CMC values varying from 1.5 mM for C4C3 to 0.05 mM for C4C12.'  They found that these surfactants could extract membrane proteins from different origins behaving as mild detergents, leading to partial extraction in some cases. They also retain protein functionality, as shown for BmrA and maintain this protein's ATPase activity. 

It would be interesting to see how many other proteins these surfactants work with.  Maybe you will see BmrA and other membrane proteins in this database built for protein membrane interactions.