Proteins Cysteine

Sulfur is a constituent of two amino acids that occur in proteins, cysteine and methionine (chapter 10), and occurs in a large number of additional natural products, several of which we will encounter in what follows. 

The nse of self-assembled monolayers of proteins by direct chemical attachment of the peptide to a modified snrface obviates some of the protein orientation difficnlties observed in the construction of LB mono-layers. An initial report of the construction of peptide SAMs on silanized qnartz was pnblished in early 1998 (185). Pilloud et al. have utilized the covalent ligation of protein cysteine thiols to thiol-terminated silanized... 

Dietary Reference Intake (DRI) of Cu, 17-18% of the DRI of K, P, and Fe, and between 5 and 13% of the DRI of Zn, Mg, and Mn (Table 5.1). Potatoes are generally not rich in Ca, but can be a valuable source of trace elements, such as Se and I, if fertilized appropriately (Eurola et al., 1989 Poggi et al., 2000 Turakainen et al., 2004 Broadley et al., 2006). Moreover, since potato tubers have relatively high concentrations of organic compounds that stimulate the absorption of mineral micronutrients by humans, such as ascorbate (vitamin C), protein cysteine and various organic and amino acids (USDA, 2006), and low concentrations of compounds that limit their absorption, such as phytate (0.11-0.27% dry matter Frossard et al., 2000 Phillippy et al., 2004) and oxalate (0.03% dry matter Bushway et al., 1984), the bioavailability of mineral elements in potatoes is potentially high. 

Fig. 6.18. Cubane-type Fe4S4 cluster. The total charge can be +3, +2, or +1 depending on the oxidation states of the iron ions. The cluster shown in the figure is coordinated to four protein cysteines, giving total charge of —1, —2, or —3, respectively.

Protein name pl MW Full length Signal peptide Activation peptide Mature protein Cysteines Substrate specificity5... 

Scheme 15 Oxidation states of protein cysteines and labeling of 1,3-cyclohexadiones with sulfeninc acids...

The most common chemoselective conjugation is achieved through thiol coupling to free cysteine (C) groups via maelimide chemistry. In proteins, cysteine residues make up only 1.7% of amino acids, and because they tend to... 

Table 5. Protein cysteine protease inhibitor (CPI) proteins.

Arabidopsis thaliana (mouse-ear cress) (Brassicaceae) FL3-27 (gene) (proprotein 11 kDa stress-induced homologue of cowpea cysteine protease inhibitor protein) Cysteine protease inhibitor protein (cystatin) homologue [148]... 

The methodology of peptide mapping by RP-HPLC is straightforward. The protein is first denatured and reduced with urea and dithiothreitol (DTT), respectively, to unfold the protein. Cysteine residues are then blocked... 

In many of the haemoproteins we shall be discussing, the protoporphyrin IX group is held to the polypeptide chain only by hydrogen bonding, Van der Wools forces and iron-protein bonds. In several other cases, notably in cytochrome-c and its related compounds, the haem is covalently linked to the protein via substituents at the pyrrole carbon atoms. Cyto-chrome-c can be regarded as an iron protoporphyrin IX group with the addition of a protein cysteine side-chain across the vinyl double bonds giving two thio-ether links (Fig. 3). 

Pantothenic acid has a central role in energy-yielding metabolism as the functional moiety of coenzyme A (CoA), in the biosynthesis of fatty acids as the prosthetic group of acyl carrier protein, and through its role in CoA in the mitochondrial elongation of fatty acids the biosynthesis of steroids, porphyrins, and acetylcholine and other acyl transfer reactions, including postsynthetic acylation of proteins. Perhaps 4% of all known enzymes utilize CoA derivatives. CoA is also bound by disulfide links to protein cysteine residues in sporulating bacteria, where it may be involved with heat resistance of the spores, and in mitochondrial proteins, where it seems to be involved in the assembly of active cytochrome c oxidase and ATP synthetase complexes. 

Cystatin refers to a diverse family of protein cysteine protease inhibitors. There are three general types of cystatins Type 1 (stefens), which are primarily found in the cytoplasm but can appear in extracellular fluids Type 2, which are secreted and found in most extracellular fluids and Type 3, which are multidomain protease inhibitors containing carbohydrates and that include the kininogens. Cystatin 3 is used to measure renal function in clinical chemistry. See Barrett, A.J., The cystatins a diverse superfamily of cysteine peptidase inhibitors, Biomed. Biochim. Acta 45,1363-1374,1986 Katunuma, N., Mechanisms and regulation of lysosomal proteolysis, Revis. Biol. Cellular 20, 35-61, 1989 Gauthier, F., Lalmanach, G., Moeau, T. et al., Cystatin mimicry by synthetic peptides, Biol Chem. Hoppe Seyler 373, 465-470, 1992 Bobek, L.A. and Levine,... 

Many pathways exist to generate a nitrosothiol in vitro by the 1-electron oxidation of NO. Nitrosothiols can be formed via the reaction of a thiol with N2O3, a nitrosating agent that is an intermediate in the decomposition of NO in aerobic solution, or via the direct reaction of NO with a thiol to form an addition complex (SNO ) followed by a 1-electron oxidation. S-nitrosation of a protein thiol also can occur by a trans-S-nitrosation event from a low molecular weight nitrosothiol, such as S -nitrosoglutathione, or from a nitrosated protein cysteine (8). Whereas the in vivo mechanism of protein S -nitrosation is unknown, a protein-mediated trans-S -nitrosation mechanism is an attractive possibility because of the specificity it could impart on the reaction. Additionally, the same protein could catalyze both the nitrosation and denitrosation of a specific cysteine. A report showing that the protein thioredoxin can transnitrosate caspase-3 selectively and reversibly lends support to this proposal (34). 

Metallothionein protein, found extensively in the brain, contains zinc, and so does cysteine-rich intestinal protein (cysteine is an amino acid). RNA proteins contain zinc as part of their structures. RNA, a protein, directs cellular protein synthesis using patterns taken from the DNA in the cell nucleus. 

Fig. 1 Glutathionylation as reversible inactivation of signaling proteins. A protein cysteine...

---