The structure of the aquaporin-1 water channel: a comparison between cryo-electron microscopy and X-ray crystallography.
Three different medium-resolution structures of the human water channel aquaporin-1 (AQP1) have been solved by cryo-electron microscopy (cryo-EM) during the last two years. Recently, the structure of the strongly related bovine AQP1 was solved by X-ray crystallography at higher resolution, allowing a validation of the original medium-resolution structures, and providing a good indication for the strengths and limitations of state of the art cryo-EM methods. We present a detailed comparison between the different models, which shows that overall, the structures are highly similar, deviating less than 2.5 A from each other in the helical backbone regions. The two original cryo-EM structures, however, also show a number of significant deviations from the X-ray structure, both in the backbone positions of the transmembrane helices and in the location of the amino acid side-chains facing the pore. In contrast, the third cryo-EM structure that included information from the X-ray structure of the homologous bacterial glycerol facilitator GlpF and that was subsequently refined against cryo-EM AQP1 data, shows a root mean square deviation of 0.9A from the X-ray structure in the helical backbone regions.
de Groot
Bert L
BL
Theoretical Molecular Biophysics Group, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. bgroot@gwdg.de
Engel
Andreas
A
Grubmüller
Helmut
H
D000818:Animals; D051398:Aquaporin 1; D020346:Aquaporins / Q000737:chemistry* / Q000235:genetics; D001789:Blood Group Antigens; D002417:Cattle; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D006801:Humans; D015394:Molecular Structure; D005810:Multigene Family; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
C496020:AQP1 protein, human; D020346:Aquaporins; D001789:Blood Group Antigens; D051398:Aquaporin 1