Evolutionary and developmental differences in delta-crystallin from bird and reptile lenses Circular dichroism and fluorescence studies

Abstract

1. 1. Delta-crystallin has been isolated by preparative isoelectric focusing from embryonic and/or adult lenses of the chicken, quail, turkey, duck, caiman and gecko. The secondary and tertiary structures of the delta-crystallins were examined by circular dichroism (CD) spectroscopy in the near- and far-ultraviolet and by fluorescence spectroscopy. 2. 2. Age-dependent differences were observed in the structure of delta-crystallin in the chicken and the turkey. Adult delta-crystallin had less alpha-helical structure when examined by far-ultraviolet CD spectroscopy, less rotatory strength in the near ultraviolet and less fluorescence when excited at 280 nm than embryonic delta crystalline. Despite these spectral differences, embryonic and adult chicken delta-crystallins behaved similarly when subjected to sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis, gel filtration and isoelectric focusing in a sucrose density gradient. 3. 3. Far-ultraviolet CD spectroscopy indicated that delta-crystallin from the embryonic chicken, quail and turkey was approximately 80% alpha-helical, while that from embryonic duck was about 40% alpha-helical. By contrast, delta-crystallin from the adult chicken and turkey had about 30% alpha-helix, and that from adult caiman and gecko had about 30% and 10% alpha-helic, respectively. The near-ultraviolet CD spectra of the embryonic chicken, quail and turkey were similar, while that of the embryonic duck was related in structure but had less rotatory strength and resembled the profile of delta-crystallin from adult chicken, turkey and gecko. The fluorescence spectra of delta-crystallins from all species examined had emission maxima at 315 nm after excitation at 280 nm and 295 nm. There were species-dependent and age-dependent differences in intensity of the fluorescence spectra. Taken together, the data indicate considerable conservation of the conformation of delta-crystalline throughout evolution.