title: Molecular portrait of lens gap junction protein MP70.
abstract: A 70-kDa membrane protein (MP70) is a component of the lens fiber gap junctions. Its membrane topology and its N-terminal sequence are similar to those of the connexin family of proteins. Some features of MP70 containing fiber gap junctions are, however, distinct from gap junctions in other mammalian tissues: (i) Lens connexons form crystalline arrays only after cleavage of junctional proteins in vitro. These hexagonal arrays have a periodicity of 13.6 nm which is significantly larger than the 8- 9-nm spacing of liver and heart gap junctions. (ii) Lens fiber gap junctions dissociate in low concentrations of nonionic detergent and this provides an avenue to purify MP70 directly from a membrane mixture. Isolated MP70 in the form of 17 S structures has an appearance consistent with connexon pairs. (iii) The C-terminal half of MP70 is cleaved in situ by a lens endogenous calcium-dependent protease. The processed from MP38 remains in the membrane and is abundant in the central region of the lens. A testable hypothesis for MP70 function is presented.
authors.affiliation: Department of Cellular & Molecular Biology, University of Auckland, New Zealand.
authors.forename: J
authors.initials: J
authors.lastname: Kistler
authors.forename: J
authors.initials: J
authors.lastname: Berriman
authors.forename: C W
authors.initials: CW
authors.lastname: Evans
authors.forename: W T
authors.initials: WT
authors.lastname: Gruijters
authors.forename: D
authors.initials: D
authors.lastname: Christie
authors.forename: A
authors.initials: A
authors.lastname: Corin
authors.forename: S
authors.initials: S
authors.lastname: Bullivant
mesh_terms: D017630:Connexins; D003902:Detergents; D004591:Electrophoresis, Polyacrylamide Gel; D005136:Eye Proteins / Q000302:isolation & purification / Q000648:ultrastructure*; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D008562:Membrane Glycoproteins / Q000648:ultrastructure*; D008565:Membrane Proteins / Q000648:ultrastructure; D008854:Microscopy, Electron; D011487:Protein Conformation; D000099264:Connexin 50
chemical_list: D017630:Connexins; D003902:Detergents; D005136:Eye Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D000099264:Connexin 50