Phosphoproteins

Casein ( ; from Latin caseus, 'cheese') is a family of related phosphoproteins (αS1, aS2, β, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in human milk. Sheep and cow milk have a higher casein content than other types of milk with human milk having a particularly low casein content.

thumb|Serine in an amino acid chain, before and after phosphorylation.

protein-coding gene in the species Homo sapiens

28 kDa heat- and acid-stable phosphoprotein is a protein that in humans is encoded by the PDAP1 gene.