Structure
Lacritin consists of 119 amino acids after cleavage of the N-terminal signal peptide and displays several predicted alpha helices, mostly in the C-terminal half. At least one appears to be amphipathic with hydrophobic and hydrophilic residues on opposite faces. The hydrophobic face likely forms the binding site for syndecan-1. PONDR (Predictor of Naturally Disordered Regions) predicts that the C-terminal and N-terminal halves are respectively 'ordered' and 'disordered'. 11 - 12 predicted O-glycosylation sites populate the N-terminal half. One putative amphipathic alpha helix near the C-terminus may be responsible for binding the N-terminus of syndecan-1, and is the site of lacritin's only N-glycosylation site. In 'climatic droplet keratopathy' this site appears to be unglycosylated. Predicted pI of lacritin's core protein is 5.
Several lacritin splice variants have been detected in Aceview, from NEIBank EST data. Lacritin-b (11.1 kDa; pI 5.3) lacks the sequence SIVEKSILTE. Lacritin-c (10.7 kDa; pI 4.6) displays a novel C-terminus that should be incapable of binding syndecan-1. Both may be null forms of lacritin.
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