title: Affinity tags can reduce merohedral twinning of membrane protein crystals.
abstract: This work presents a comparison of the crystal packing of three eukaryotic membrane proteins: human aquaporin 1, human aquaporin 5 and a spinach plasma membrane aquaporin. All were purified from expression constructs both with and without affinity tags. With the exception of tagged aquaporin 1, all constructs yielded crystals. Two significant effects of the affinity tags were observed: crystals containing a tag typically diffracted to lower resolution than those from constructs encoding the protein sequence alone and constructs without a tag frequently produced crystals that suffered from merohedral twinning. Twinning is a challenging crystallographic problem that can seriously hinder solution of the structure. Thus, for integral membrane proteins, the addition of an affinity tag may help to disrupt the approximate symmetry of the protein and thereby reduce or avoid merohedral twinning.
authors.affiliation: Department of Chemical and Biological Engineering, Chalmers University of Technology, PO Box 462, SE-40530 Gothenburg, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Backmark
authors.forename: Maria
authors.initials: M
authors.lastname: Nyblom
authors.forename: Susanna
authors.initials: S
authors.lastname: Törnroth-Horsefield
authors.forename: Urszula
authors.initials: U
authors.lastname: Kosinska-Eriksson
authors.forename: Kristina
authors.initials: K
authors.lastname: Nordén
authors.forename: Maria
authors.initials: M
authors.lastname: Fellert
authors.forename: Per
authors.initials: P
authors.lastname: Kjellbom
authors.forename: Urban
authors.initials: U
authors.lastname: Johanson
authors.forename: Kristina
authors.initials: K
authors.lastname: Hedfalk
authors.forename: Karin
authors.initials: K
authors.lastname: Lindkvist-Petersson
authors.forename: Richard
authors.initials: R
authors.lastname: Neutze
authors.forename: Rob
authors.initials: R
authors.lastname: Horsefield
mesh_terms: D000345:Affinity Labels / Q000737:chemistry* / Q000378:metabolism; D020346:Aquaporins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods; D006801:Humans; D010843:Pichia; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018724:Spinacia oleracea
chemical_list: D000345:Affinity Labels; D020346:Aquaporins; D010940:Plant Proteins; D011994:Recombinant Proteins