Exploring the restless nanostructures in the cell membrane: Single molecule approach

Ken Ritchie and Akihiro Kusumi

Dept. of Biological Science, Nagoya University, Nagoya, Japan
and Kusumi Membrane Organizer Project (ERATO), JST, Nagoya, Japan

The plasma membrane of living cells is a dynamic 2-D fluid of embedded mobile and immobile objects (lipids and proteins) with a sub-surface scaffolding (the membrane skeleton) and a forest of sugars and secreted proteins on the extracellular surface. We are applying single molecule probes to help elucidate the fine structure of this complex system. The free diffusion of membrane proteins (visualized through specifically attaching a colloidal gold probe) implies a compartmentalized structure where the membrane cytoskeleton and its associated proteins form kinetic barriers to diffusion. By applying a subtle hand (optical tweezers) to move the constituents around, we can further, directly examine the membrane's structure. Direct imaging of these barriers, and consequentially the membrane skeleton, has been accomplished through scanning optical force microscopy using a single transmembrane protein probe and combining the positional accuracy of single colloidal gold tracking with the ultra-soft spring of the optical trap.