Subunit composition of delta-crystallin from embryonic chick lens. Analysis of methionine-containing tryptic peptides and cyanogen bromide peptides

Purification, properties, and cellular localization of Euglena ferredoxin-NADP reductase

Ferredoxin-NADP reductase from Euglena gracilis Klebs var. Bacillaris Cori purified to apparent homogeneity, yields a typical 36 kDa and an unusual 15 kDa polypeptide on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, exhibits a typical flavoprotein spectrum, contains FAD, and catalyzes NADPH-dependent iodonitrotetrazolium-violet diaphorase, NADPH-specific ferredoxin-dependent cytochrome-c-550 reductase and NADPH-NAD transhydrogenase activities. Rabbit antibody to the purified FNR blocks these activities specifically and also blocks the iodonitrotetrazolium-violet diaphorase activity of Euglena chloroplast completely. The low iodonitrotetrazolium-violet diaphorase activity in the plastidless mutant, W10BSmL, is mitochondrial and is not specifically blocked by the ferredoxin-NADP reductase antibody. Dark-grown non-dividing (resting) wild-type Euglena cells show a 4-fold increase in ferredoxin-NADP reductase activity during greening at 970 lx. Half of the low ferredoxin-NADP reductase activity in dark-grown cells is initially soluble, but by the end of chloroplast development nearly all of the enzyme is membrane-bound. The binding of ferredoxin-NADP reductase on exposure to light correlates with the extent of thylakoid membrane formation. Immunoblots of wild-type extracts during greening indicate that the 15 kDa polypeptide increases in the same manner as the extent of reductase binding to thylakoid membranes.

Two delta-crystallin polypeptides are derived from a cloned delta 1-crystallin cDNA

Previous studies have shown that there are 2 similar delta-crystallin genes (delta 1 and delta 2) and at least 2 delta-crystallin polypeptides in the chicken eye lens. We show here that both delta-crystallin polypeptides can be synthesized from mRNA transcribed in vitro from a cloned delta 1-crystallin cDNA. Both polypeptides co-migrate in SDS-urea-polyacrylamide electrophoresis with their authentic counterparts isolated from 15-day-old embryonic chicken lenses, and both react with sheep anti-chicken delta-crystallin serum. Screening nearly 900 delta-crystallin cDNA clones from a 15-day-old embryonic lens library with an oligonucleotide probe specific for exon 2 of the delta 2-crystallin gene failed to detect any delta 2 cDNA clones, indicating that the delta 2 gene produces little or no mRNA in the lens at this stage of development. Our results suggest that both of the observed delta-crystallin polypeptides are derived from mRNA transcribed from the delta 1 gene, with heterogeneity arising at the translational or co-translational level.

Characterization and crystallization of delta-crystallin from the eye lens of adult turkey: comparison with delta-crystallin from adult quail and young chick

delta-Crystallin, purified from either adult turkey or quail lenses, and characterized by amino acid composition and circular dichroism spectroscopy, is shown to be similar to delta-crystallin purified from 3-day-old chick lenses. Crystallization of turkey delta-crystallin is reported along with the characterization of the crystal unit cell by X-ray diffraction techniques. Variation in unit cell parameters is observed and is correlated with hydration.

Gene and protein structure of a beta-crystallin polypeptide in murine lens: relationship of exons and structural motifs

A 23,000 molecular weight beta-crystallin (beta 23) of the murine eye lens is encoded in a 4.1 +/- 0.3-kilobase gene containing three introns. Each of the four exons seems to code for a separate structural motif of the protein, whose tertiary structure was predicted by an interactive computer graphics technique based on the crystallographic structure of bovine gamma II-crystallin. The first exon also encodes a hydrophobic N-terminal peptide resembling membrane anchor sequences of other proteins. Our results indicate structural homology among the beta- and gamma-crystallin polypeptides, and link gene structure with protein structure in this superfamily of lens proteins.

Structural and functional similarities of delta-crystallin messenger ribonucleic acids from duck and chicken lenses

delta-Crystallin of the embryonic duck lens was compared with that of the embryonic chicken lens with respect to polypeptide composition, synthesis, and messenger ribonucleic acid (mRNA) sequences. Labeling experiments with [35S]methionine revealed that the duck delta-crystallin is composed of minor amounts of polypeptides with molecular weights near 50000 (50K) and 49000 (49K) and much greater amounts of polypeptides with molecular weights near 48000 (48K) and 47000 (47K), as judged by sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis. All four sizes of polypeptides were synthesized in similar relative proportions as found in vivo in a rabbit reticulocytes lysate supplemented with delta-crystallin mRNA isolated from the embryonic duck lens. Synthesis of the 48K and 47K delta-crystallin polypeptides was differentially reduced in duck lenses cultured in the presence of ouabain. This is similar to the differential reduction of synthesis of the lower molecular weight delta-crystallin peptides in embryonic chicken lenses demonstrated previously. R loops formed between duck or chicken delta-crystallin mRNA and a cloned chicken delta-crystallin cDNA and heteroduplexes formed between duck or chicken delta-crystallin mRNA and cloned chicken genomic DNAs containing delta-crystallin sequences showed that, except for the putative 5' leader sequence, the duck and chicken delta-crystallin mRNAs have extremely similar nucleotide sequences. These data indicate considerable conservation of delta-crystallin throughout the approximately 100 million years of divergence between ducks and chickens. The findings also suggest a possible relationship between the structure of delta-crystallin mRNA and the differential reduction in synthesis of the lower molecular weight delta-crystallin polypeptides in ouabain-treated lenses of ducks and chickens.

Regulation of protein synthesis, intracellular electrolytes and cataract formation in vitro

Control of protein synthesis is associated with changes in the ratio of intracellular Na+ to K+ in the cultured embryonic chick lens. Correlations of intracellular Na+/K+ ratios with crystallin synthesis and cataract formation in vitro suggest that the Na+/K+ ratio may have an important role in the regulation of protein synthesis during cataractogenesis.

Partial dissociation and renaturation of embryonic chick delta-crystallin. Characterization by ultracentrifugation and circular dichroism

1. delta-Crystallin from 15-day-old embryonic chick lenses was characterized by circular dichrosim (CD) spectroscopy. Examination by CD spectroscopy in the far ultraviolet (190-250 nm) demonstrated that the secondary structure of delta-crystallin has at least 75% alpha-helix; the delta-crystallin subunits dissociated in sodium dodecyl sulfate retain their alpha-helical content. This appreciable alpha-helical content of delta-crystallin contrasts with the absence of alpha-helix in other lens crystallins. 2. As judged by CD spectroscopy in the near ultraviolet (250-320 nm) the tertiary structure of embryonic delta-crystallin is not readily disrupted by environmental changes, such as NaCl, KSCN or the non-ionic detergent Emulphogene BC 720, and is stable to temperature fluctuation between 2 and 56 degrees C. 3. Experiments were directed towards deaggregation and renaturation of the four subunits of embryonic delta-crystallin by treatment with urea or guanidine hydrochloride. The native tertiary structure of delta-crystallin was lost above 4 M urea or 2 M guanidine hydrochloride, as judged by CD spectroscopy in the near ultraviolet. Ultracentrifugation at sedimentation equilibrium showed that in 4 M urea delta-crystallin dissociates into dimeric subunits, while in 2 M guanidine hydrochloride delta-crystallin exists as a mixture of dimeric and tetrameric subunits. Dialysis of delta-crystallin from 4 M urea resulted in reaggregation of the subunits into tetramers, about 50% of which showed native tertiary structure. Dialysis from 2 M guanidine hydrochloride also resulted in tetramer formation, and about 35% was recovered with native conformation. Removal of denaturant by dialysis produced no native teritary structure after treatment with 8 M urea, but about 15% native conformation after treatment with 6 M guanidine hydrochloride.