Table 2.

Membrane-Associated Mucins Expressed at the Human Ocular Surface

Symbol	Total amino acids of protein backbone	Predicted mass of protein backbone	Number of Isoforms listed in NCBI Gene	Number of amino acids in cytoplasmic tail
MUC16	14,507	1,519 kDa	14	31
MUC4	7,418	734 kDa	4	22
MUC22	1,786	175 kDa	3	92
MUC20	709	72 kDa	4	N/A*
MUC21	626	60 kDa	3	66
MUC1	484**	50 kDa	20	72

Protein data derived from the NCBI Protein database; listed here is the amino acid number of the longest isoform identified in the database

Estimated molecular weight of the protein backbone mass was computed using:https://web.expasy.org/compute_pi/

^*MUC20 is membrane-associated, but does not appear to be transmembrane

^**A longer isoform of MUC1, thus far only identified in cancer cells (1255 amino acids) is listed in the UniProtKB database