Resolution of translation start site for the human Kell glycoprotein

The human Kell blood group system currently contains 35 antigens determined by allelic polymorphisms in the Kell glycoprotein, a single-pass Type II transmembrane protein. The Kell glycoprotein was initially cloned through screening of a cDNA library; however, direct amino acid sequencing of most of the Kell glycoprotein has not been reported. The N-terminus of the Kell glycoprotein contains two potential translational start sites, which result in differences in the cytoplasmic tail.

Protein extracts were isolated from human red blood cell membranes and were digested with trypsin. The resulting peptides were subjected to liquid chromatography-tandem mass spectrometry, allowing resolution of peptides from the N-terminus of the Kell glycoprotein.

Peptides were isolated and sequenced that correspond to the upstream methionine start site predicted by the full cDNA sequence. No evidence of internal translation initiation at Methionine 20 was detected.

These findings identify the translational start site and define the full cytoplasmic tail of the human Kell glycoprotein.