Biomaterial Database

Acetylation of alpha-crystallin with N-acetylimidazole and its influence upon the native aggregate and subunit reassembly. 1999

J K Pal, and S K Bera, and S K Ghosh

Crystallography & Molecular Biology Division, Saha Institute of Nuclear Physics 1/AF Bidhannagar, 700064, Calcutta, India.

OBJECTIVE An attempt has been made to investigate the involvement and importance of some of the hydrogen bond forming amino acid side chains in intra and inter subunit interactions in alpha-crystallin assembly. METHODS For this, alpha-crystallin has been acetylated, partially or completely, using N-acetylimidazole. The apparent molecular size, electrophoretic mobility, conformational properties, surface hydrophobicity and chaperone activity of the modified proteins have been determined and compared with those of unmodified native protein as well as of the aggregates reassembled from the modified subunits. RESULTS Acetylation of the surface-exposed tyrosine side chains has been found to destabilize the integrity of the native assembly with the formation of a somewhat smaller aggregate. This acetylated aggregate appears to adopt a molten globule-like conformation as evidenced from its almost unaltered secondary structure with some detectable alterations in its tertiary structure as well as from its enhanced chaper-one activity exhibited by the reduction assay compared to the native alpha-crystallin. Reassociation studies from either partially or completely acetylated subunits indicate that acetylation perturbs the information needed for native refolding of the subunits from their unfolded state as well as that needed for the normal mode of subunit reassembly. Acetylated subunits exhibit abnormal gel electrophoretic band pattern with distinctly retarded migration compared to the unmodified subunits. However, in spite of the partial/complete acetylation of the subunits or their reassociation from the denatured state, the tryptophan fluorescence emission maxima of the modified proteins and also that of the reassociated aggregates appear to remain unaffected. CONCLUSIONS Results tend to indicate that the unperturbed hydrogen bonding capability of the relevant side chains in alpha-crystallin is needed for the integrity of the native alpha-crystallin assembly, for the normal refolding of its denatured subunits and also for the correct mode of subunit reassembly.

UI	MeSH Term	Description	Entries
D007093	Imidazoles	Compounds containing 1,3-diazole, a five membered aromatic ring containing two nitrogen atoms separated by one of the carbons. Chemically reduced ones include IMIDAZOLINES and IMIDAZOLIDINES. Distinguish from 1,2-diazole (PYRAZOLES).
D011487	Protein Conformation	The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).	Conformation, Protein,Conformations, Protein,Protein Conformations
D011489	Protein Denaturation	Disruption of the non-covalent bonds and/or disulfide bonds responsible for maintaining the three-dimensional shape and activity of the native protein.	Denaturation, Protein,Denaturations, Protein,Protein Denaturations
D002850	Chromatography, Gel	Chromatography on non-ionic gels without regard to the mechanism of solute discrimination.	Chromatography, Exclusion,Chromatography, Gel Permeation,Chromatography, Molecular Sieve,Gel Filtration,Gel Filtration Chromatography,Chromatography, Size Exclusion,Exclusion Chromatography,Gel Chromatography,Gel Permeation Chromatography,Molecular Sieve Chromatography,Chromatography, Gel Filtration,Exclusion Chromatography, Size,Filtration Chromatography, Gel,Filtration, Gel,Sieve Chromatography, Molecular,Size Exclusion Chromatography
D002942	Circular Dichroism	A change from planar to elliptic polarization when an initially plane-polarized light wave traverses an optically active medium. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)	Circular Dichroism, Vibrational,Dichroism, Circular,Vibrational Circular Dichroism
D003459	Crystallins	A heterogeneous family of water-soluble structural proteins found in cells of the vertebrate lens. The presence of these proteins accounts for the transparency of the lens. The family is composed of four major groups, alpha, beta, gamma, and delta, and several minor groups, which are classed on the basis of size, charge, immunological properties, and vertebrate source. Alpha, beta, and delta crystallins occur in avian and reptilian lenses, while alpha, beta, and gamma crystallins occur in all other lenses.	Lens Proteins,Crystallin,Eye Lens Protein,Lens Protein, Eye,Protein, Eye Lens,Proteins, Lens
D004591	Electrophoresis, Polyacrylamide Gel	Electrophoresis in which a polyacrylamide gel is used as the diffusion medium.	Polyacrylamide Gel Electrophoresis,SDS-PAGE,Sodium Dodecyl Sulfate-PAGE,Gel Electrophoresis, Polyacrylamide,SDS PAGE,Sodium Dodecyl Sulfate PAGE,Sodium Dodecyl Sulfate-PAGEs
D006041	Goats	Any of numerous agile, hollow-horned RUMINANTS of the genus Capra, in the family Bovidae, closely related to the SHEEP.	Capra,Capras,Goat
D006860	Hydrogen Bonding	A low-energy attractive force between hydrogen and another element. It plays a major role in determining the properties of water, proteins, and other compounds.	Hydrogen Bonds,Bond, Hydrogen,Hydrogen Bond
D000107	Acetylation	Formation of an acetyl derivative. (Stedman, 25th ed)	Acetylations