What are posttranslational modifications of proteins ?
A.
In addition to folding properly, many proteins—once they leave the ribosome—require further adjustments before they are useful to the cell. Namely, many proteins require posttranslational modifications (PTMs) to become fully functional.
B.
To be useful to the cell, a completed polypeptide must fold correctly into its three-dimensional conformation and then bind any required cofactors and protein partners—all via noncovalent bonding.
C.
Many proteins also require one or more covalent modifications to become active—or to be recruited to specific membranes or organelles.
D.
Although phosphorylation and glycosylation are the most common, more than 100 types of covalent modifications of proteins are known.