title: The fold of human aquaporin 1.
abstract: The fold of human aquaporin 1 is determined from cryo-electron microscopic data at 4.5 A resolution. The monomeric structure consists of two transmembrane triple helices arranged around a pseudo-2-fold axis connected by a long flexible extracellular loop. Each triplet contains between its second and third helix a functional loop containing the highly conserved fingerprint NPA motif. These functional loops are assumed to fold inwards between the two triplets, thereby forming the heart of the water channel. The helix topology was determined from the directionality pattern of each of the six transmembrane helices with respect to the membrane, together with constraints defined by the sequence and atomic force microscopy data. The directionality of the helices was determined by collecting the best-fitting orientations resulting from a search through the three-dimensional experimental map for a large number of alpha-helical fragments. Tests on cryo-electron crystallographic bacteriorhodopsin data suggest that our method is generally applicable to determine the topology of helical proteins for which only medium-resolution electron microscopy data are available.
authors.affiliation: Theoretical Molecular Biophysics Group, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen, D-37077, Germany.
authors.forename: B L
authors.initials: BL
authors.lastname: de Groot
authors.forename: J B
authors.initials: JB
authors.lastname: Heymann
authors.forename: A
authors.initials: A
authors.lastname: Engel
authors.forename: K
authors.initials: K
authors.lastname: Mitsuoka
authors.forename: Y
authors.initials: Y
authors.lastname: Fujiyoshi
authors.forename: H
authors.initials: H
authors.lastname: Grubmüller
mesh_terms: D051398:Aquaporin 1; D020346:Aquaporins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D001436:Bacteriorhodopsins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D001789:Blood Group Antigens; D020285:Cryoelectron Microscopy; D006801:Humans; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D017510:Protein Folding; D017433:Protein Structure, Secondary
chemical_list: C496020:AQP1 protein, human; D020346:Aquaporins; D001789:Blood Group Antigens; D010446:Peptide Fragments; D051398:Aquaporin 1; D001436:Bacteriorhodopsins