Interaction of alpha-crystallin with lens plasma membranes. Affinity for MP26.
The binding of the major water-soluble lens protein alpha-crystallin to the lens plasma membrane has been investigated by reassociating purified alpha-crystallin with alpha-crystallin-depleted membranes and with phospholipid vesicles in which the lens membrane protein MP26 had been reconstituted. alpha-Crystallin reassociates at high affinity (Kd = 13 X 10(-8)M) with alkali-washed lens plasma membranes but not with lens plasma membranes treated with guanidine/HCl, nor with phospholipid vesicles or erythrocyte membranes. Binding to lens plasma membranes is dependent on salt, temperature and pH and occurs in a saturable manner. Reconstitution of MP26 into phospholipid vesicles and subsequent analysis of alpha-crystallin binding suggests the involvement of this transmembrane protein. Binding ist not influenced by pretreatment of membranes with proteases, suggesting that the 4-kDa cytoplasmic fragment of MP26 is not necessary for alpha-crystallin binding. Labeling experiments using (trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine as a probe for intrinsic membrane proteins further showed that alpha-crystallin contains hydrophobic regions on its surface which might enable this protein to make contact with the lipid bilayer. Newly synthesized alpha-crystallin, in lens culture, is not associated with the plasma membrane, suggesting that the assembly of alpha-crystallin aggregates does not take place in a membrane-bound mode.
D000818:Animals; D020346:Aquaporins; D001389:Azirines; D002413:Cations, Divalent; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D003459:Crystallins / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007908:Lens, Crystalline / Q000378:metabolism*; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000378:metabolism*; D009994:Osmolar Concentration; D011485:Protein Binding; D013696:Temperature
D020346:Aquaporins; D001389:Azirines; D002413:Cations, Divalent; D003459:Crystallins; D005136:Eye Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C030328:aquaporin 0; C033174:3-(trifluoromethyl)-3-(3-iodophenyl)diazirine