Cysteine residues crosslinking

Insulin, a small protein of molecular mass 6000 daltons, is composed of two chains designated A and B. There are no reduced cysteine residues in insulin, but it contains three essential disulfide bonds two that crosslink the A and B chains, and one internal to the A chain to stabilize the overall tertiary stmcture. These disulfide bonds are cleaved in the presence of excess AuX4, leaving A and B chains that have cysteine residues that have become oxidized to sulfonic adds [119]. With smaller amounts of AuX4, a single disulfide bond will be attacked to form sulfinic acid [119]. The reaction is second order for AuCU while AuBr4 reacts too quickly for accurate monitoring. 

In view of the high affinity of arsenic for thiol functions, it can be expected that lewisite and CVAA will bind to cysteine residues of proteins. When human blood was incubated with 20 nM to 0.2 mM of [14C]lewisite, 25-50% of the dose became associated with globin (35). Electrospray tandem MS provided evidence for the presence of a CVAA-crosslink between the cysteine-93 and cysteine-112 residues in fi-globin. Whether this was the only type of adduct has not yet been completely elucidated. It must be remarked, however, that this result was in contrast with results obtained by others for the analogous phenyldichloroarsine, for which binding to human hemoglobin could not be observed. 

Elastic fibers form the network in skin and cardiovascular tissue (elastic arteries) that is associated with elastic recovery. Historically the recovery of skin and vessel wall on removal of mechanical loads at low strains has been attributed to elastic fibers. Elastic fibers are composed of a core of elastin surrounded by microfibrils 10 to 15 nm in diameter composed of a family of glycoproteins recently termed fibrillins. Fibrillins are a family of extracellular matrix glycoproteins (MW about 350,000) containing a large number of cysteine residues (cysteine residues form disulfide crosslinks). Several members of the family have been described. The common molecular features include N and C terminal ends with 47 tandemly repeated epi-... 

Some amino acid units other than the 20 discussed above are formed by reactions on existing protein molecules. For example, the thiol (SH) groups in two cysteine residues can be oxidized to a disulfide linkage (-S-S-) and produce a cystine unit. If the two cysteine residues are on different chains, this reaction links the two chains in what is called a chemical crosslink. This is shown in Equation 2. The squiggly lines indicate that the cysteine units are located along a polymer chain. 

Several conclusions can be reached from this study. First, multiple GroEL apical domains indeed bind to substrate polypeptides, both in vivo and in vitro, and this ability appears to be crucial to the cellular function of GroEL. This is supported by the additional demonstration that non-native Rubisco bound to a GroEL containing an apical cysteine residue made disulfide crosslinks to multiple GroEL subunits. Second, different substrates have different requirements for the apical domains, stringent substrates such as MDH and Rubisco being the most... 

This work began with our preparation of a 30-residue polypeptide having the sequence K(IEALEGK)(IEALEPalK)(IEACEGK)(IEALEGK)G which places the non-natural amino acid 4-pyridyl alanine (Pal) at position 14 of the sequence this is the most solvent-exposed f position of the second heptad repeat (72). An additional feature of this sequence is that it incorporates a cysteine residue at position 19 (a hydrophobic d position) in order to allow for the introduction of an inter-chain disulfide bond crosslink to ensure that this peptide forms a stable two-stranded coiled-coil. 

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