Glycation of lens MIP26 affects the permeability in reconstituted liposomes

We studied the role of glycation of lens putative gap junctional protein, MIP26, on the permeability as well as on calmodulin mediated gating activity in reconstituted liposomes. Calf lens membranes were incubated with 0-100 mM glucose for 3 days and MIP26 was isolated. There was a glucose concentration dependent increase in the glycation of MIP26 which reached to 2.48 moles/mole of protein with 100 mM glucose. Gel electrophoresis showed that there was no degradation of MIP26 to MIP22 during incubation. Channel permeability was determined by reconstituting MIP26 into asolectin liposomes. There was a MIP26 glycation dependent decrease in the permeability to sucrose. Furthermore, proteoliposomes containing nonglycated MIP26 showed complete uncoupling of the channels with calmodulin whereas the channels containing glycated MIP26 were only partially uncoupled. These results suggest that glycation of MIP26 does interfere with the gating activity in reconstituted liposomes.