Cysteine
•Substitutions:
Cysteine shows no preference generally for substituting with any other amino acid, though it can tolerate
substitutions with other small amino acids.
Largely the above preferences can be accounted for
by the extremely varied roles that Cysteines play in proteins (see below). The substitutions preferences
shown above are derived by analysis of
all Cysteines, in all contexts, meaning that what are really quite varied preferences are averaged and
blurred; the result being quite
meaningless.
•Role in structure: The role of
Cysteines in structure is very dependent on
the cellular location of the protein in which they are contained. Within extracellular proteins, cysteines are frequently
involved in disulphide bonds, where
pairs of cysteines are oxidised to form a covalent bond.
These bonds serve mostly to stabilise the protein structure, and the structure of many extracellular
proteins is almost entirely determined by
the topology of multiple disulphide bonds