The study of the binding of
alpha-crystallin to membranes is potentially important for understanding the function of
alpha-crystallin in the ocular lens and the formation of
cataracts. Using fluorescence probes, N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-glycero-3 -
phosphoethanolamine, triethylammonium
salt (
NBD-PE) and (1,1'-bi(4-anilino)
naphthalene-5,5'-disulfonic
acid, dipotassium
salt (
bis-ANS), the temperature dependence of the binding of
alpha-crystallin to
sphingomyelin liposomes, and the structural changes of
alpha-crystallin and
sphingomyelin induced by temperature were studied. The influence of the binding of
alpha-crystallin on the mobility of the head group region of
liposomes of
sphingomyelin was dependent on the thermal history of
alpha-crystallin. Binding of
alpha-crystallin to
sphingomyelin caused a decrease in the anisotropy of the fluorophore
NBD-PE at or below 37 degrees C. However, when
alpha-crystallin or the mixture of
alpha-crystallin/
sphingomyelin were preincubated near the secondary structure phase transition temperature of 60 degrees C, an increase of the anisotropy of
NBD-PE (decrease of
lipid head group mobility) was observed when measured at 22 degrees C or 37 degrees C. An inflection near 47 degrees C in the curve of fluorescence anisotropy of
bis-ANS pre-incorporated into the
alpha-crystallin corresponded to a 3 degrees or 4 degrees structural change of
alpha-crystallin.
alpha-Crystallin either increases or decreases the flexibility of the head group of
sphingomyelin liposomes depending on its structure.