Table II

Estimated number of proteins in the human proteome as a result of different classifications

Class of proteinSizeDescription
Nonredundant proteins20,000–25,000A representative protein from every gene locus
Protein variants50,000–500,000Different proteins obtained by splicing or proteolysis
Combinatorial variants>10,000,000Different proteins that are generated by somatic DNA rearrangements
Protein species>100,000Proteins that differ in chemical composition due to PTMs
Protein alleles75,000–150,000Proteins that differ by genetic variation giving amino acid differences (coding single nucleotide polymorphisms)