Linked from
The 8 pages that link to Serine, each with the reason it gives.
TyrosineCompared with: Serine can also be phosphorylated, but lacks tyrosine's aromatic ring.
Protein kinaseRelated: Many protein kinases modify serine residues.
Protein phosphorylationRelated: Its hydroxyl group is a common target for protein phosphorylation.
ThreonineCompared with: Serine shares threonine's hydroxyl chemistry but has a shorter side chain.