Molecular portrait of lens gap junction protein MP70.
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.
Kistler
J
J
Department of Cellular & Molecular Biology, University of Auckland, New Zealand.
Berriman
J
J
Evans
C W
CW
Gruijters
W T
WT
Christie
D
D
Corin
A
A
Bullivant
S
S
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
D017630:Connexins; D003902:Detergents; D005136:Eye Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D000099264:Connexin 50