By default Prot pi handels proteins assuming all cystein side chains are reduced to free sulfhydryl. Disulfide bonds are usually formed in proteins secreted to the extracellular medium. Therefore disulfide bonds can be specified as a modification, so that cystein is treated as halfcystine. Lit.
Iodoacetamide reacts covalently with the side-chain thiol group of cysteine. It is often used to modify SH-groups to prevent the re-formation of disulfide bonds after the reduction of cystine residues to cysteine.
Iodoacetic acid reacts covalently with the side-chain thiol group of cysteine. It is often used to modify SH-groups to prevent the re-formation of disulfide bonds after the reduction of cystine residues to cysteine.
Nonenzymatic deamidation of asparagines is a common modification of proteins. Deamidation proceeding through the formation fo succinimide intermediate followed by hydrolysis results in the formation of isoaspartate and aspartate in a molar ratio of approximately 3:1.
Glycation is the result of typically covalent bonding of a protein with a sugar molecule, such as fructose or glucose, without the controlling action of an enzyme. Glucose reacts with proteins through the formation of a Schiff base between the aldehyde group of glucose and the primary amines of lysine and the N-terminus of the protein.
Hydroxyproline is produced by hydroxylation of the amino acid proline by the enzyme prolyl hydroxylase following protein synthesis (as a post-translational modification). Hydroxyproline is a major component of the protein collagen and plays a key roles for collagen stability. The sequence of collagen often follows the pattern Gly-Xaa-Hyp.
Nonenzymatic deamidation of asparagines is a common modification of proteins. Deamidation proceeding through the formation fo succinimide intermediate followed by hydrolysis results in the formation of isoaspartate and aspartate in a molar ratio of apporximately 3:1.
A post-translational modification of proteins in which a serine, threonine or tyrosine residue is phosphorylated by a protein kinase by the addition of a covalently bound phosphate group.
Carbamylation of lysine and cysteine residues and free N-termini is a nonenzymatic PTM that has been related to protein ageing. It can be artificially introduced during sample preparation with urea, thus affecting studies directed toward in vivo carbamylation. In aqueous solution, urea is in equilibrium with ammonium and isocyanate. The latter can react with primary amines of free N-termini and ε-amine groups of lysines and cysteine sulfhydryls to form carbamyl derivatives.
N-terminal acetylation is one of the most common co-translational covalent modifications of proteins in eukaryotes, and it is crucial for the regulation and function of different proteins. Lit.
In bacteria and organelles, the initiation of protein synthesis is signaled by the formation of formyl-methionyl-tRNA (tRNAfMet). fMet is only used for the initiation of protein synthesis and is thus found only at the N terminus of the protein. Once protein synthesis is accomplished, the formyl group on methionine can be removed by peptide deformylase. Lit.
Amidation (in vivo) is a common post-translational modification in peptides and peptide hormones
in which the N-Cα bond of a C-terminal glycine is cleaved in two steps by the bifunctional enzyme
PAM, resulting in an amidated C-terminus. Lit.
Protein methylation, catalyzed by highly specific methyltransferase enzymes, is a relatively common post-translational modification and plays an important role in various biological processes. Monomethylation occurs most frequently at arginine and lysine residues. Lit.
Protein methylation, catalyzed by highly specific methyltransferase enzymes, is a relatively common post-translational modification and plays an important role in various biological processes. Dimethylation occurs most frequently at arginine and lysine residues. Lit.
Protein methylation, catalyzed by highly specific methyltransferase enzymes, is a relatively common post-translational modification and plays an important role in various biological processes. Trimethylation occurs most frequently at lysine residues. Lit.
Sulfation is a common post-translational modification of tyrosine residues in eukaryotes, but has not been observed in yeast and prokaryotes. Sulfation is limited to secretory and transmembrane proteins that have passed the trans-Golgi network, where two membrane-bound tyrosylprotein sulfotransferase enzymes catalyze the transfer of sulfate from adenosine 3’-phosphate 5’-phosphosulfate to the tyrosine phenol. Lit.
γ-Carboxylation occurs mainly in proteins related to blood coagulation. Glutamic acid residues are carboxylated by the enzyme glutamyl carboxylase in γ-position in the presence of oxygen and carbon dioxide. Vitamin K is required as a cofactor. Lit.
S-Palmitoylation is a reversible post-translational modifaction, whereby a palmitic acid is covalently attached to cysteine residue of a protein. The reaction is catalyzed by protein palmitoyl acyltransferases. This modification strongly alters the hydrophobicity of the protein. Lit.
C-Mannosylation is a unique type of protein glycosylation. A C-C bond is formed between the C1 atom of an α-mannose and the C2 atom of the indole ring of a tryptophan residue via mannosyltransferases. Lit.
mono-ADP-ribosylation is a common post-translational modification, where an ADP-ribose moiety is transferred from NAD⁺ to the substrate protein under the release of nicotinamide. The transfer of ADP-ribose occurs onto amino acid residues with a nucleophilic oxygen, nitrogen or sulfur. Lit.
N-Myristoylation refers to the covalent linkage of a myristic acid to the N-terminal glycine via an amide bond of many eukaryotic and viral proteins. The reaction is catalyzed by N-myristoyltransferase, is irreversible and affects the hydrophobicity of the protein. Lit.
Farnesylation is a subspecies of prenylation in which a 15-carbon isoprenoid lipid is attached to a cysteine residue by farnesyltransferase. Most prenylated proteins contain a CAAX motif at the C-terminus. Lit.
Geranylgeranylation is a subspecies of prenylation in which a 20-carbon isoprenoid lipid is attached to a cysteine residue by geranlygeranyltransferase I. Most prenylated proteins contain a CAAX motif at the C-terminus. Lit.
Nitration is a post-translational modification of mostly tyrosine residues that is caused by oxidation. First, a tyrosine radical is formed by one-electron oxidation followed by a reaction with nitrogen dioxide resulting in 3-nitrotyrosine. Lit.
S-nitrosylation is a post-translational modification in which a nitric oxide molecule is bound via a reactive thiol group of a cysteine residue. S-nitrosylation has various regulatory roles in bacteria, yeasts, plants and mammalian cells. Lit.
Citrulline is a non-proteinogenic amino acid that is produced through post-translational deimination of peptidyl-arginine. Peptidyl-arginine deiminases catalyze the hydrolysis of a guanido group into an urea group. This modifications affects the formation of hydrogen bonds and therefore protein folding. Lit.
Amidation (in vitro) is an artificial modification that can be introduced at the C-terminus of a protein whereby the carboxyl group is replaced by an amide group. The C-terminal amide can be formed by chemical synthesis or by catalysation of carboxypeptidase-Y.