Enzymes
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Reaction participants Show >> << Hide
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Namehelp_outline
[protein]-L-isoaspartate
Identifier
RHEA-COMP:12144
Reactive part
help_outline
- Name help_outline L-β-isoaspartate residue Identifier CHEBI:90596 Charge -1 Formula C4H4NO3 SMILEShelp_outline N([C@@H](CC(*)=O)C([O-])=O)* 2D coordinates Mol file for the small molecule Search links Involved in 1 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline S-adenosyl-L-methionine Identifier CHEBI:59789 Charge 1 Formula C15H23N6O5S InChIKeyhelp_outline MEFKEPWMEQBLKI-AIRLBKTGSA-O SMILEShelp_outline C[S+](CC[C@H]([NH3+])C([O-])=O)C[C@H]1O[C@H]([C@H](O)[C@@H]1O)n1cnc2c(N)ncnc12 2D coordinates Mol file for the small molecule Search links Involved in 868 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
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Namehelp_outline
[protein]-L-isoaspartate α-methyl ester
Identifier
RHEA-COMP:12143
Reactive part
help_outline
- Name help_outline L-isoaspartate α-methyl ester residue Identifier CHEBI:90598 Charge 0 Formula C5H7NO3 SMILEShelp_outline N([C@@H](CC(*)=O)C(OC)=O)* 2D coordinates Mol file for the small molecule Search links Involved in 1 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline S-adenosyl-L-homocysteine Identifier CHEBI:57856 Charge 0 Formula C14H20N6O5S InChIKeyhelp_outline ZJUKTBDSGOFHSH-WFMPWKQPSA-N SMILEShelp_outline Nc1ncnc2n(cnc12)[C@@H]1O[C@H](CSCC[C@H]([NH3+])C([O-])=O)[C@@H](O)[C@H]1O 2D coordinates Mol file for the small molecule Search links Involved in 792 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
Cross-references
RHEA:12705 | RHEA:12706 | RHEA:12707 | RHEA:12708 | |
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Reaction direction help_outline | undefined | left-to-right | right-to-left | bidirectional |
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Publications
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Purification and properties of protein methylaase II.
Kim S., Paik W.K.
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Differences in alpha-Crystallin isomerization reveal the activity of protein isoaspartyl methyltransferase (PIMT) in the nucleus and cortex of human lenses.
Lyon Y.A., Sabbah G.M., Julian R.R.
Although it is well-known that protein turnover essentially stops in mature lens fiber cells, mapping out the ensuing protein degradation and its effects on lens function over time remains challenging. In particular, isomerization is a common, spontaneous post-translational modification that occur ... >> More
Although it is well-known that protein turnover essentially stops in mature lens fiber cells, mapping out the ensuing protein degradation and its effects on lens function over time remains challenging. In particular, isomerization is a common, spontaneous post-translational modification that occurs over long timescales and generates products invisible to most analytical methods. Nevertheless, isomerization can significantly impact protein structure, function, and solubility, which are all necessary to maintain clarity and proper refractive index within the lens. Herein, we examine the degree of isomerization occurring in crystallin proteins in the human eye lens as a function of both age and location within the lens. A novel mass spectrometric technique leveraging radical chemistry enables detailed characterization of proteins extracted from the cortex and nucleus of the lens. It is observed that the degree of isomerization increases significantly between the cortex and nucleus and between water-soluble and water-insoluble fractions. Interestingly, the abundance of L-isoAsp is low in the water-soluble cortex despite being the dominant product generated by isomerization of Asp in vitro, suggesting that Protein L-isoaspartyl methyltransferase (PIMT) is active in the cortex and suppresses the accumulation of L-isoAsp. The abundance of L-isoAsp increases dramatically in the nucleus, revealing that PIMT activity decreases over time in the center of the lens. In addition, the growth of L-isoAsp in the nuclear fraction suggests protein isomerization continues within the nucleus, despite the fact that most of the protein within the nucleus has become insoluble. Additionally, it is demonstrated that sequential Asp residues lead to isomerization hotspots in human crystallin proteins and that the isomerization profiles for αA and αB crystallin are notably different. Although αA is more prone to isomerization, αB loses solubility more rapidly upon modification. These differences are likely related to the distribution of Asp residues within αA and αB, which are in turn connected to refractive index. The high Asp content of αA is a hazard in terms of isomerization and aging, but it serves to enhance the refractive index of αA relative to αB, and may explain why αA is only found in the eye. << Less
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Methylation at specific altered aspartyl and asparaginyl residues in glucagon by the erythrocyte protein carboxyl methyltransferase.
Ota I.M., Ding L., Clarke S.
Protein carboxyl methyltransferases from erythrocytes and brain appear to catalyze the esterification of L-isoaspartyl and/or D-aspartyl residues but not of normal L-aspartyl residues. In order to identify the origin of these unusual residues which occur in subpopulations of a variety of cellular ... >> More
Protein carboxyl methyltransferases from erythrocytes and brain appear to catalyze the esterification of L-isoaspartyl and/or D-aspartyl residues but not of normal L-aspartyl residues. In order to identify the origin of these unusual residues which occur in subpopulations of a variety of cellular proteins, we studied the in vitro methylation by the erythrocyte enzyme of glucagon, a peptide hormone of 29 amino acids containing 3 aspartyl residues and a single asparagine residue. Methylated glucagon was digested with either trypsin, chymotrypsin, pepsin, or endoproteinase Arg C, and the labeled fragments were separated by high-performance liquid chromatography and identified. In separate experiments, methyl acceptor sites were determined by digesting glucagon first with proteases and then assaying purified glucagon fragments for methyl acceptor activity. Using both approaches, we found that the major site of methylation, accounting for about 62% of the total, was at the position of Asp-9. Chemical analysis of fragments containing this residue indicated that this site represents an L-isoaspartyl residue. A second site of methylation, representing about 23% of the total, was detected at the position of Asn-28 and was also shown to represent an L-isoaspartyl residue. Methyl acceptor sites were not detected at the positions of Asp-15 or Asp-21. Preincubation of glucagon under basic conditions (0.1 M NH4OH, 3 h, 37 degrees C) increased methylation at the Asn-28 site by 4-8-fold while methylation at the Asp-9 site remained unchanged. These results suggest that methylation sites can originate from both aspartyl and asparaginyl residues and that these sites may be distinguished by the effect of base treatment. << Less
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Protein carboxyl methyltransferases: two distinct classes of enzymes.
Clarke S.