Directed formation of lipid membrane microdomains as high affinity sites for His-tagged proteins.

Lipid membranes composed of an iminodiacetic acid functionalized lipid, DSIDA, in a POPC matrix exhibited switchable properties via Cu(2+) recognition to rapidly assemble microdomains that act as high affinity sites for His-tagged proteins. The microdomains demonstrated an order of magnitude enhanced affinity for the proteins compared to homogeneously functionalized POPC membranes with Ni(2+)-NTA DOGS or Cu(2+)-DOIDA, while a rapid release and restoration of the original membrane was accomplished with micromolar concentrations of EDTA.

Lipid nanotube formation from streptavidin-membrane binding.

A novel transformation of giant lipid vesicles to produce nanotubular structures was observed upon the binding of streptavidin to biotinylated membranes. Unlike membrane budding and tubulation processes caused by proteins involved with endocytosis and vesicle fusion, streptavidin is known to crystallize at near the isoelectric point (pI 5 to 6) into planar sheets against biotinylated films. We have found, however, that at neutral pH membranes of low bending rigidity (<10kT), such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), spontaneously produce tubular structures with widths ranging from micrometers to below the diffraction limit (<250 nm) and lengths spanning up to hundreds of micrometers.