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Biomedical subjects

L Takemoto

Publications and source records attributed to L Takemoto.

At least 19 recordsLinked to original sources
PubMed1996

Increase in the intramolecular disulfide bonding of alpha-A crystallin during aging of the human lens.

Aging of the normal human lens is accompanied by oxidation of protein sulfhydryl groups to disulfide groups. Although this has been known for many years, very little is known about the exact amino acid residues involved. In addition, almost nothing is known concerning the temporal sequence of this oxidative process over the lifetime of the individual. To address these two concerns for alpha-A crystallin, the polypeptide was purified from total proteins of the human lens, followed by digestion with lys-C endoprotease. Mass spectral analysis of the resulting fragments demonstrated that the two cysteine residues (cysteine-131 and cysteine-142) are present as a mixture of an intramolecular disulfide bond and free sulfhydryl groups. Reverse phase chromatography was used to resolve and quantitate the relative amounts of the two forms present in alpha-A crystallin from normal lenses of different age. Even in very young lenses (4 months and 5 months of age) there is significant oxidation of the two cysteine residues. However, the oxidative state of these two residues does not significantly change during the next approximately 27 years of age, after which there is an increase in the relative amount of intramolecular disulfide bonding. Together, these results have identified and quantitated the relative change in the oxidative state of two specific cysteine residues of alpha-A crystallin in human lenses of different age, and have established that age-dependent oxidation of these two residues occurs primarily during the later part of life.

Adolescent↗
PubMed1996

EM immunolocalization of alpha-crystallins: association with the plasma membrane from normal and cataractous human lenses.

PURPOSE: To integrate past biochemical findings with past morphological observations of area insoluble material isolated from cataract and aged normal lenses, by determining the spatial distribution of alpha-crystallins associated with the plasma membrane (PM) of nuclear cataractous and age matched normal human lenses. METHODS: Lenses were homogenized, pelleted and washed several times in 0.05M Tris-Cl (pH 7.2) containing 100mM KCl, 1 mM MgCl2 and 2mM beta-mercaptoethanol, followed by several washes in 8M urea. Urea insoluble pellets (UIP) were labeled before fixation and embedding with rabbit serum raised against alpha-crystallins, followed by goat anti-rabbit IgG conjugated to 5nm gold. Approximately 300 gold particles associated with the PM were counted, for each lens, on several electron microscopy (EM) micrographs. The number of gold particles/um of PM, number of individual vs clusters of gold particles were determined. RESULTS: Micrographs from both normal and cataractous human lenses clearly demonstrated the association of alpha-crystallins with the PM. Also apparent was the abundant labeling of the PM for cataractous lenses as compared to normal lenses. Quantification of the gold labeling revealed that not only was there an increase in the amount of labeling/um of PM in cataract lenses, but there was also an increased percentage of gold in clusters. These clusters were not only more numerous in cataractous lenses, but also contained a greater number of gold/cluster. CONCLUSIONS: These findings provide morphological evidence that the PM in nuclear cataract lenses is associated with large aggregates of alpha-crystallin.

Aged↗
PubMed1995

The mutation Asp69-->Ser affects the chaperone-like activity of alpha A-crystallin.

alpha-Crystallins are members of the family of small heat-shock proteins. The conformation and mode of action of these 'junior chaperones' are unknown. To investigate the structure and chaperone-like activity, four mutants of bovine alpha A-crystallin were generated by site-directed mutagenesis. In comparison with wild-type alpha A-crystallin, the D69S mutant, in which a highly conserved charged residue has been replaced, forms larger multimers and displays a threefold reduced heat-protection capacity. The conformation and thermal stability of this mutant are not noticeably affected. Three other mutations, replacing hydrophobic by uncharged hydrophilic residues, were aimed at disturbing hydrophobic intersubunit interactions. None of these mutations resulted in major structural perturbations and only minor differences in heat-protective capacity were observed. Although it is assumed that small heat-shock proteins interact with denaturing proteins via their hydrophobic surfaces, this study clearly shows that charged residues in alpha-crystallin can also influence the efficiency of substrate binding.

Amino Acid Sequence↗
PubMed1995

Age-dependent cleavage at the C-terminal region of lens beta B2 crystallin.

A previous study has demonstrated that in vivo, the peptide bonds at the C-terminal region of the alpha-A crystallins were cleaved in an age-dependent manner, between the two hydroxyl-containing amino acids in the sequence -PS(T)S (Takemoto, 1995). Bovine beta B2 crystallin also contains the sequence-PSS at its C-terminus. To determine if this specific site of cleavage occurred in other lens proteins besides alpha-A crystallin, beta B2 crystallin was prepared from total proteins of young versus adult bovine lens fiber cells. After cleavage by cyanogen bromide, the C-terminal fragments were characterized by mass spectrometry. The results showed that peptide cleavage also occurred between the two hydroxyl-containing amino acids in the sequence -PSS of beta B2 crystallin from older fiber cells, demonstrating that age-dependent cleavage of this peptide bond occurs in multiple proteins of the aging lens.

Age Factors↗
PubMed1994

Binding of denatured protein decreases the chaperone properties of alpha crystallin.

Previous studies have demonstrated that partially denatured forms of the beta and gamma crystallins preferentially bind to a central region of the alpha crystallin particle, both in vitro and in vivo. These experiments were designed to ascertain if binding of a partially denatured protein to alpha crystallin could result in a diminished ability of alpha crystallin to protect against further protein denaturation and aggregation. A constant amount of alpha crystallin was incubated with increasing amounts of purified gamma s crystallin and then heated at 65 degrees C for 45 min. Under these conditions, the partially denatured gamma s crystallin binds to alpha crystallin. The resulting complexes were tested for their ability to protect against heat-induced denaturation and aggregation of alcohol dehydrogenase heated at 44 degrees C. As increasing amounts of partially denatured gamma s bound to alpha crystallin, the resulting complexes possessed a decreased ability to protect against heat-induced denaturation and aggregation. These results demonstrate that binding of partially denatured forms of a purified protein to alpha crystallin results in a complex with decreased ability to protect against denaturation, suggesting a possible mechanism whereby the molecular chaperone properties of alpha crystallin may be diminished in vivo.

Alcohol Dehydrogenase↗
PubMed1994

Characterization of the alpha-gamma and alpha-beta complex: evidence for an in vivo functional role of alpha-crystallin as a molecular chaperone.

Previous studies have demonstrated that in vitro, alpha-crystallin can protect other lens proteins against extensive denaturation and aggregation. The mechanism of this protection involves preferential binding of the partially denatured protein to a central region of the native alpha-crystallin complex. To test whether a similar phenomenon might occur in vivo, a high molecular weight aggregate (HMWA) fraction was isolated from the aged bovine lens. Negative staining of this preparation revealed the presence of particles of 13-14 nm diameter, characteristic of alpha-crystallin. Immunolocalization of the same particles using antiserum specific for gamma- and beta-crystallins demonstrated preferential binding of these crystallins to the central region of the alpha-crystallin complex. Together, these results provide evidence that in the intact lens, the alpha-crystallins are functionally important molecular chaperones.

Animals↗
PubMed1994

Immunolocalization of the C-terminal and N-terminal regions of alpha-A and alpha-B crystallins.

The C-terminal and possibly the N-terminal regions of the alpha crystallins are thought to be involved in the molecular chaperone properties of the protein. To localize these regions within the 13-15 nm aggregate of native alpha crystallin, antisera specific for the C-terminal and N-terminal regions were used together with immunogold and transmission electron microscopy. The results demonstrate that the C-terminal regions of the alpha-A and alpha-B molecules and the N-terminal regions of the alpha-A and/or alpha-B molecules are localized to a central region of the native alpha aggregate. These findings demonstrate that the C-terminal and N-terminal regions of alpha crystallin are localized to a region of the alpha aggregate that has previously been hypothesized to be the binding site for partially denatured proteins.

Animals↗
PubMed1994

Alpha-A crystallin: quantitation of C-terminal modification during lens aging.

Previous studies have demonstrated that the C-terminal region of alpha-A crystallin is susceptible to age-dependent, posttranslational modification. To quantitate the amount of modification, alpha-A crystallin was purified from total proteins of the aging bovine lens, then digested with lys-C endoproteinase. Reverse phase, high pressure liquid chromatography was used to resolve and quantitate the resulting peptides, to determine the amount of C-terminal peptide relative to peptides from other regions of the protein that have not been reported to undergo modification. The results indicate that relative to alpha-A crystallin from newborn lens, posttranslational modification has occurred in approximately 45-55% of the C-terminal region from mature lens. These results demonstrate extensive modification of the C-terminal region of alpha-A crystallin from the mature lens, indicating that during the aging process, posttranslational modifications in this region may make significant contributions to the aggregated state and/or molecular chaperone properties of the molecule.

Aging↗
PubMed1994

Molecular chaperone properties of the high molecular weight aggregate from aged lens.

The high molecular weight aggregate (HMWA) fraction was isolated from the water soluble proteins of aged bovine lenses. Its composition and ability to inhibit heat-induced denaturation and aggregation were compared with the lower molecular weight, oligomeric fraction of alpha isolated from the same lens. Although the major components of both fractions were the alpha-A and alpha-B chains, the HMWA fraction possessed a decreased ability to protect other proteins against heat-induced denaturation and aggregation. Immunoelectron microscopy of both fractions demonstrated that alpha particles from the HMWA fraction contained increased amounts of beta and gamma crystallins, bound to a central region of the supramolecular complex. Together, these results demonstrate that alpha crystallins found in the HMWA fraction possess a decreased ability to protect against heat-induced denaturation and aggregation, and suggest that at least part of this decrease could be due to the increased presence of beta and gamma crystallins complexed to the putative chaperone receptor site of the alpha particles.

Alcohol Dehydrogenase↗
PubMed1994

Preferential interaction of alpha crystallin with denatured forms of gamma crystallin.

PURPOSE: To characterize the possible interaction of alpha crystallin with partially denatured forms of gamma crystallin. METHODS: Gamma crystallin was denatured in the presence of guanidine hydrochloride, then dialyzed in the presence or absence of alpha crystallin. The high-molecular-weight complex formed in the presence of alpha was characterized by gel filtration chromatography, electron microscopy, and quantitative Western blot analysis. RESULTS: Relative to native alpha or reconstituted aggregates of purified alpha, the higher molecular weight complex possessed a greater mean diameter and contained increased amounts of gamma crystallin. CONCLUSIONS: Alpha crystallin preferentially interacts with partially denatured forms of a lens protein, consistent with its putative role as a functional molecular chaperone in the intact lens.

Animals↗
PubMed1993

The C-terminal region of alpha-crystallin: involvement in protection against heat-induced denaturation.

Recent studies have demonstrated that the alpha-crystallins can protect other proteins against heat-induced denaturation and aggregation. To determine the possible involvement of the C-terminal region in this activity, the alpha-crystallins were subjected to limited tryptic digestion, and the amount of cleavage from the N-terminal and C-terminal regions of the alpha-A and alpha-B crystallin chains was assessed using antisera specific for these regions. Limited tryptic digestion resulted in cleavage only from the C-terminal region of alpha-A crystallin. This trypsin-treated alpha-A crystallin preparation showed a decreased ability to protect proteins from heat-induced aggregation using an in vitro assay. Together, these results demonstrate that the C-terminal region of alpha-A crystallin is important for its ability to protect against heat-induced aggregation, which is consistent with the hypothesis that post-translational changes that are known to occur at the C-terminal region may have significant effects on the ability of alpha-A crystallin to protect against protein denaturation in vivo.

Alcohol Dehydrogenase↗
PubMed1993

Localization of the chaperone binding site.

The hypothesis derived from models of the multi-oligomeric chaperone complex suggests that partially denatured proteins bind in a central cavity in the aggregate. To test this hypothesis, the molecular chaperone, alpha crystallin, was bound to partially denatured forms of gamma crystallin, and the binding site was visualized by immunogold localization. In an alternative approach, gold particles were directly complexed with gamma crystallin, followed by binding to the alpha crystallin aggregate. In both cases, binding was localized to the central region of the aggregate, confirming for the first time that partially denatured proteins do indeed bind to a central region of the molecular chaperone aggregate.

Animals↗
PubMed1992

Age-dependent loss of the C-terminal amino acid from alpha crystallin.

Antiserum made against the C-terminal region of alpha-A crystallin was used to monitor the purification of a tryptic peptide containing the C-terminus of the molecule from fetal versus adult bovine lenses. Mass spectral analysis of the peptide preparations obtained from these lenses demonstrated the presence of a peptide (T20) containing an intact C-terminus from fetal lenses and the presence of an additional peptide (T20') from older lenses that contained a cleaved C-terminal serine. These results demonstrate an age-dependent processing of alpha-A crystallin in the bovine lens, resulting in removal of the C-terminal amino acid residue.

Aging↗
PubMed1992

Oxidation of the N-terminal methionine of lens alpha-A crystallin.

Antiserum against the N-terminal peptide of bovine alpha-A crystallin has been used to monitor purification of two different seropositive peptides (i.e. T1a and T1b) from a tryptic digest of bovine lens proteins. Both these peptides have similar amino acid compositions, but peptide T1b has a molecular weight 16 atomic mass units larger than T1a, suggesting posttranslational modification. Analysis of ionization fragments of the T1b peptide by mass spectrometry demonstrates that this difference in molecular weight is due to the in vivo oxidation of the N-terminal met residue of the alpha-A crystallin molecule.

Amino Acid Sequence↗
PubMed1992

The ability of lens alpha crystallin to protect against heat-induced aggregation is age-dependent.

Alpha crystallin was prepared from newborn and aged bovine lenses. SDS-PAGE and tryptic peptide mapping demonstrated that both preparations contained only the alpha-A and alpha-B chains, with no significant contamination of other crystallins. Compared with alpha crystallin from the aged lens, alpha crystallin from the newborn lens was much more effective in the inhibition of beta L crystallin denaturation and precipitation induced in vitro by heat. Together, these results demonstrate that during the aging process, the alpha crystallins lose their ability to protect against protein denaturation, consistent with the hypothesis that the alpha crystallins play an important role in the maintenance of protein native structure in the intact lens.

Aging↗
PubMed1992

Binding of actin to lens alpha crystallins.

Actin has been coupled to a cyanogen bromide-activated Sepharose 4B column, then tested for binding to alpha, beta, and gamma crystallin preparations from the bovine lens. Alpha, but not beta or gamma, crystallins bound to the actin affinity column in a time dependent and saturable manner. Subfractionation of the alpha crystallin preparation into the alpha-A and alpha-B species, followed by incubation with the affinity column, demonstrated that both species bound approximately the same. Together, these studies demonstrate a specific and saturable binding of lens alpha-A and alpha-B with actin.

Actins↗