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R C Augusteyn

Publications and source records attributed to R C Augusteyn.

77 records · Page 5Linked to original sources
PubMed1971

-Crystallin. The isolation and characterization of distinct macromolecular fractions.

alpha-Crystallin was isolated from calf lens periphery by chromatography on DEAE-cellulose and gel filtration. Three distinct populations of macromolecules have been isolated with molecular weights in the ranges approx. 6x10(5)-9x10(5), 0.9x10(6)-4x10(6) and greater than 10x10(6). The concentration of macromolecules at the molecular-weight limits of a population are very low. The members of the different populations do not appear to be in equilibrium with each other. Further, in those molecular-weight fractions investigated, no equilibrium between members of the same population was observed. The population of lowest molecular weight comprises 65-75% of the total material. The amino acid and subunit composition of the different-sized fractions appear very similar, if not identical. The only chemical difference observed between the fractions is the presence of significant amounts of sugar in the higher-molecular-weight fractions. Subunit molecular weights of approx. 19.5x10(3) and 22.5x10(3) were observed for all alpha-crystallin fractions.

Amino Acids↗
PubMed1971

-Crystallin. Fractionation of subunits and sequence studies on an isolated polypeptide.

alpha-Crystallin was carboxymethylated with radioactive iodoacetic acid in the presence of 7.6m-urea and then separated into six major fractions by chromatography on DEAE-cellulose in 7m-urea. Based on the amino acid compositions, specific radioactivities and sodium dodecyl sulphate-gel electrophoresis of the fractions, it was concluded that alpha-crystallin contains at least four different subunits: DU1A and DU1B, containing no cysteine; a third component represented by DU2B and DU3 containing one cysteine one cysteine residue per subunit; and DU4, which probably contains two residues of cysteine per subunit. Subunit DU1A was shown to be of sufficient purity for sequence studies. Cyanogen bromide cleavage yielded two peptides, CB-1 and CB-2, in approximately equal amounts as expected. The sum of the molecular weights and amino acid compositions of the peptides were both in excellent agreement with the results obtained for subunit DU1A. The amino acid sequence of the first sixteen residues of peptide CB-1 is: Ser-Leu-Thr-Lys-Asp-Phe-Asp-Glu-Val-Asn-Ile-Asp-Val-Ser-His-Phe-. The sequence of the first seventeen residues of peptide CB-2 is: Asp-Ile-Ala-Ile-Ser-His-Pro-Trp-Ile-Arg-Pro-Ser-Phe-Phe-Glu-Phe-His-. The N-terminal sequence of subunit DU1A was shown to be N-acetylmethionine followed by peptide CB-2.

Amino Acid Sequence↗
PubMedDate not supplied

alpha-Crystallin polymers and polymerization: the view from down under.

Several models have been proposed for the quaternary structure of alpha-crystallin. Some suggest the subunits are arranged in concentric shells. Others propose that the subunits are in a micelle-like arrangement. However, none is able to satisfactorily account for all observations on the protein and the quaternary structure of alpha-crystallin remains to be established. In this review, factors contributing to the assembly and polymerization are examined in order to evaluate the different models. Consideration of the variations in particle size and molecular weight under different conditions leads to the conclusion that alpha-crystallin cannot be a micelle or a layered structure. Instead, it is suggested that the protein may be assembled from a 'monomeric' unit comprising eight subunits arranged in two tetramers with cyclic symmetry. The octameric unit is proposed to be disc-like particle with a diameter of 9.5 nm and a height of 3 nm. The larger particles, chains and sheet-like structures commonly observed are assembled from the octamers. Structural predictions indicate that the polypeptide may be folded into three independent domains which have different roles in the structural organization and functions of the protein. It is suggested that the tetramers are stabilized through interactions involving the second domain (residues 64-104) while assembly into the octamers and higher polymers requires hydrophobic interactions involving the N-terminal domain. Deletion of parts of this domain by site directed mutagenesis revealed that residues 46-63 play a critical role in the assembly. Current research aims to identify the specific amino acids involved.

Amino Acid Sequence↗