Disulphide bond formation

Martin, J.E., Bardwell, J.C.A., Kuriyan, J. Crystal structure of the DsbA protein required for disulphide bond formation in vivo. Nature 365 464-468, 1993. 

Origami K-12 trxBIgor mutant, greatly facilitates cytoplasmic disulphide bond formation... 

Disulphide bond formation between 2 Cys residues Myristoylation C-terminal amide formation Biotinylation... 

Another modification to the ricin precursor which occurs during or immediately after synthesis is disulphide bond formation [124]. In mature ricin, the B chain contains four intrachain disulphide bonds and it is joined to the A chain by a single interchain bond. These disulphide bonds are formed enzymically by ER protein disulphide isomerase [134, 135] which introduces five intrachain disulphide bonds into nascent proricin, the bond destined to become the interchain disulphide bond joining the A and B chains of mature ricin being formed between cysteine residues present in the A- and B-chain sequences in the proricin. 

The absolute purity of a biological substance is hard - if at all possible - to determine. Regular and sometimes only subtle protein modifications such as glycosyla-tion, alternative disulphide bond formation, deamidation, oxidation, phosphorylation, acetylation, sulfation, sulfoxidation, y-carboxylation, and pyroglutamate formation lead to protein variants that may have more or less different characteristics. Also, truncated protein variants might be generated by the presence of cryptic or alternative start sites of transcription, by premature stop of the peptide chain... 

It is also possible that disulphide bond formation and rearrangement occurs after excretion of the protein from its cell of synthesis in some cases. This would best account for assembly of very large sulphur-rich aggregates such as hair. Exact cross linking fidelity is probably not so critical in these cases and complete assembly of such large cross-linked meshworks within a cell is clearly impossible. 

Many of the post-translational modifications observed in bacterial cells also occur to eukaryotic proteins. These include disulphide bond formation, hydroxylation, glycosylation, phosphorylation and cleavage of precursor forms to mature proteins. 

---