W0423

Structural Studies of Lactose permease from E. coli. Jeff Abramson, Irina Smirnova, Gill Verner, Vladimir Kasho, Bernadette Byrne, So Iwata, Ron Kaback, Dept. of Biological Sciences, Imperial College London, Exhibition Rd., London, SW7 2AZ UK.

Transport proteins are a principal class of integral membrane proteins, many of which transduce the free energy stored in electrochemical ion gradients into substrate concentration gradients across a membrane. One large group of evolutionary related transport proteins is the Major Facilitator Superfamily (MFS). Members of this superfamily are found in membranes of a wide range of species ranging from archaea to the mammalian central nervous system and catalyse the transport of various solutes. An important model for MFS function is the lactose permease (LacY) in the Escherichia coli cytoplasmic membrane which is composed of 417 amino-acid residues and presumed to form 12 transmembrane spanning helices. A profusion of biochemical and mutagenesis studies have been performed on this protein making it arguably one of the best studied of all membrane proteins. However understanding of the precise mechanism of action of LacY has so far been limited by a lack of high resolution structural data. We currently have two crystal forms of LacY which diffract to 3.5 /5.0 Å and 2.9 /4.0 Å (anisotropic diffraction). The first crystal form belongs to the P6₂22 space group with cell dimensions of a=b=86.4Å c=415.9Å while the second crystal form is P2₁2₁2₁ with cell dimensions a=103.1 b=126.9 c=188.7. Structural determination is currently under progress.