Methionine residue

Methionyl hGH. The first form of hGH to be produced through recombinant DNA technology was actually a derivative of hGH having one additional methionine residue at its N-terminus (11). Although technology has advanced to the stage where natural sequence hGH can easily be produced, as of this writing this derivative, referred to as methionyl hGH, is stiU produced commercially. 

Sulfoxide hGH. Methionine residues in proteins are susceptible to oxidation primarily to the sulfoxide. Both pituitary-derived and biosynthetic hGH undergo sulfoxidations at Met-14 and Met-125 (29). Oxidation at Met-170 has also been reported in pituitary but not biosynthetic hGH. Both desamido hGH and Met-14 sulfoxide hGH exhibit full biological activity (29). 

FIGURE 21.13 The structure of mitochou-dtial cytochrome c. The heme is shown at the center of the structure, covalently linked to the protein via its two sulfur atoms (yellow). A third sulfur from a methionine residue coordinates the iron. 

Proteins can be cleaved specifically at the amide bond on the carboxyl side of methionine residues by reaction with cyanogen bromide. BrC=N. 

TABLE 2. Proteins and peptides whose biological activity is affected by oxidation of methionine residues ... 

Ribosomal protein L12 was oxidized with 0.3 M H202 at 30°C for 1 h. After dialysis, the protein was incubated in the presence of 0.8 M 2-mercaptoethanol for 48 min at 37 °C and dialyzed. The amount of methionine residues was quantitated by exhaustive alkylation of the protein with [14C]iodoacetic acid. 

Human somatotropin 191 amino acids E. coll Pituitary dwarfism Approved for sale If useful in treatment of osteoporosis then market size will be much larger Has additional methionine residue at N-terminus, but technology for removing this now available... 

Alpha-l-antiprotease (ai-AP) limits tissue damage arising from the actions of the leucocyte protease, elastase (Carrell and Travis, 1985), and there is much evidence available for the oxidative inactivation of this protein by oxygen-derived free-radical species and hypochlorous acid/hypochlorite anion (HOCl/OCP). The mechanism of this inactivation appears to involve the oxidation of a critical methionine residue (Met-358) to its corresponding sulphoxide and methionine sulphoxide has been detected in ai-AP samples isolated from the lungs of cigarette smokers (Carp et al., 1982) and rheumatoid synovial fluids (Wong and Travis, 1980). 

Garner, M.H. and Spector, A. (1980). Selective oxidation of cysteine and methionine residues in normal and senile cataractous lenses. Proc. Natl Acad. Sci. USA 77, 1274-1277. 

Human G6PD had been purified and characterized (Yl), and the structure of the cDNA and genomic clone has also been identified (M12, Pll, T6). The monomer of G6PD consists of 515 amino acids including the initial methionine residue. Only the tetrameric or dimeric forms composed of a single type subunit are catalytical-ly active. In human red blood cells, the dimers are the predominant form. The en-... 

The introduction of redox activity through a Co11 center in place of redox-inactive Zn11 can be revealing. Carboxypeptidase B (another Zn enzyme) and its Co-substituted derivative were oxidized by the active-site-selective m-chloroperbenzoic acid.1209 In the Co-substituted oxidized (Co111) enzyme there was a decrease in both the peptidase and the esterase activities, whereas in the zinc enzyme only the peptidase activity decreased. Oxidation of the native enzyme resulted in modification of a methionine residue instead. These studies indicate that the two metal ions impose different structural and functional properties on the active site, leading to differing reactivities of specific amino acid residues. Replacement of zinc(II) in the methyltransferase enzyme MT2-A by cobalt(II) yields an enzyme with enhanced activity, where spectroscopy also indicates coordination by two thiolates and two histidines, supported by EXAFS analysis of the zinc coordination sphere.1210... 

Selective cleavage of peptides and proteins is an important procedure in biochemistry and molecular biology. The half-life for the uncatalyzed hydrolysis of amide bonds is 350 500 years at room temperature and pH 4 8. Clearly, efficient methods of cleavage are needed. Despite their great catalytic power and selectivity to sequence, proteinases have some disadvantages. Peptides 420,423,424,426 an(j proteins428 429 can be hydrolytically cleaved near histidine and methionine residues with several palladium(II) aqua complexes, often with catalytic turnover. 

The N-terminal methionine residue of protein can also be employed for selective PEGylation using aldehyde-terminated PEG via a reductive amination reaction, because the N-terminal primary amine has a lower pAa of 7.8 than other amines such as lysines, whose pZa is 10.1 [7]. After reaction with aldehyde-terminated PEG at low pH, the resultant imine is reduced with sodium cyanoborohydrate to provide PEGylated protein (Fig. 4) [8, 9]. This technique was used for the production of Neulasta, which was approved for use by the FDA in 2002 [10]. 

Fig. 4 PEGylation at the N-terminal methionine residue. The difference in pKa. between the N-terminal amine and other amines in the protein enables site-specific PEGylation. After reaction with aldehyde-terminated PEG at low pH, reduction of the resultant imine produces PEGylated protein...

Vithayathil, P.J., and Richards, F.M. (1960) Modification of the methionine residue in the peptide component of ribonuclease-S./. Biol. Chem. 235, 2343-2351. 

Expressing recombinant proteins as N-terminal fusions with ubiquitin [109] is another strategy that can help to achieve proper folding. Additionally, this is an elegant way to obtain proteins that do not start with a methionine residue, since the ubiquitin moiety is cleaved off by endogenous ubiquitin-specific proteases [100]. 

Contrary to LDL, high-density lipoproteins (HDL) prevent atherosclerosis, and therefore, their plasma levels inversely correlate with the risk of developing coronary artery disease. HDL antiatherogenic activity is apparently due to the removal of cholesterol from peripheral tissues and its transport to the liver for excretion. In addition, HDL acts as antioxidants, inhibiting copper- or endothelial cell-induced LDL oxidation [180], It was found that HDL lipids are oxidized easier than LDL lipids by peroxyl radicals [181]. HDL also protects LDL by the reduction of cholesteryl ester hydroperoxides to corresponding hydroperoxides. During this process, HDL specific methionine residues in apolipoproteins AI and All are oxidized [182]. 

Chen et al. [47] demonstrated that the reaction of HOC1 with cytochrome c increased cytochrome peroxidase activity by the oxidation of the methionine residue. Methionine oxidation also significantly decreased the efficiency of cytochrome c as a mitochondrial electron carrier. HOC1, HOBr, and HOI are also able to oxidize (Fen)cytochrome c [48],... 

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