title: Preliminary atomic force microscopy study of two-dimensional crystals of lactose permease from Escherichia coli.
abstract: Lactose permease (LacY) of Escherichia coli is not only a paradigm for secondary transporters but also for difficulties in two-dimensional (2D) crystallization. In this work we present the progresses achieved in the observation of 2D crystals of wild-type LacY by atomic force microscopy (AFM). Crystals were obtained following reconstitution of LacY in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes. Proteolipid sheets (PLSs) 6.4 nm in height were obtained after spreading the samples onto mica. Observations were carried out in liquid medium and in contact mode (CM-AFM). When the crystalline surfaces of the PLSs were imaged regular packing arrangements were observed. The back-Fourier transformation revealed the existence of various orientations mostly consistent with crystals possessing p2 symmetry and unit-cell dimensions: a=13.15 nm, b=16.74 nm, gamma=116 degrees. The characteristics, size, and shape of the repetitive motif could be compatible with dimers of this protein. These preliminary results are compared and discussed with previously reported 2D crystals observed by electron microscopy.
authors.affiliation: Departament de Fisicoquímica, Universitat de Barcelona, E-08028-Barcelona, Spain.
authors.forename: Sandra
authors.initials: S
authors.lastname: Merino-Montero
authors.forename: Oscar
authors.initials: O
authors.lastname: Domènech
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Montero
authors.forename: Jordi
authors.initials: J
authors.lastname: Hernández-Borrell
mesh_terms: D003460:Crystallization; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology*; D005583:Fourier Analysis; D008081:Liposomes / Q000737:chemistry*; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000648:ultrastructure; D018625:Microscopy, Atomic Force / Q000379:methods; D010713:Phosphatidylcholines / Q000737:chemistry*; D011487:Protein Conformation; D011510:Proteolipids / Q000737:chemistry
chemical_list: D008081:Liposomes; D026901:Membrane Transport Proteins; D010713:Phosphatidylcholines; D011510:Proteolipids; C021499:lactose permease; C028694:1-palmitoyl-2-oleoylphosphatidylcholine