Raman spectra of bird and reptile lens proteins

Abstract

Lenses of birds and several reptiles have been examined by Raman spectroscopy of intact lenses and some chick lens protein fractions to elucidate the relationship between chemical structure and various unusual properties of these lenses. The δ-crystallin, which is the major protein by far of young bird and reptile lenses, and which is unique to these classes, exists in situ and after chromatography chiefly in the α-helical conformation, in contrast to the lens proteins of all other species examined. This determination by Raman spectroscopy for several species of these two classes has been confirmed by circular dichroism studies of chick lens δ-crystallin. Raman spectroscopy also reveals the glycogen in pigeon lens nucleus and its absence in chicken lens and in pigeon annular pad. A comparison of the spectrum of heat-coagulated δ-crystallin as a powder with the spectrum of native δ-crystallin reveals a considerable conversion of the α-helical form to the β-pleated sheet. This is the first case in which a major conformational change has been shown to be associated with the formation of lens opacification.