The structure of GlpF, a glycerol conducting channel.
The passage of water or small neutral solutes across the cell membrane in animals, plants and bacteria is facilitated by a family of homologous membrane channels, variously known as aquaporins though perhaps more correctly as aquaglyceroporins. The glycerol facilitator (GlpF) is a 28 kDa aquaglyceroporin that catalyses transmembrane diffusion of glycerol and certain linear polyhydric alcohols in Escherichia coli. X-ray crystallographic analysis of GlpF to 2.2 A resolution revealed an alpha-barrel structure, surrounded by six full-length transmembrane helices and two half-spanning helices that are joined head-to-head in the middle of the membrane. These helices are arranged to a quasi twofold manner relative to the central membrane plane, where highly conserved residues make helix-to-helix contacts that stabilize the relative position and orientation of the helices in the structure. This sequence-structure correlation suggests that the evolutionary divergence of aquaporins and aquaglyceroporins is constrained by a conserved structural framework within which specialized function may be developed. Three glycerol molecules were resolved in the central channel through the GlpF monomer, thereby defining a transmembrane channel for glycerol permeation. The structure of glycerol GlpF complex provides insight into the chemical basis for transmembrane selective permeability.
Fu
Dax
D
Biology Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
Libson
Andrew
A
Stroud
Robert
R
D000595:Amino Acid Sequence; D020346:Aquaporins / Q000737:chemistry*; D017124:Conserved Sequence; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D005990:Glycerol; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary
D020346:Aquaporins; D029968:Escherichia coli Proteins; C078043:GlpF protein, E coli; D005990:Glycerol