Identification of a novel secretory leukocyte protease inhibitor-binding protein involved in membrane phospholipid movement.

Previous studies have suggested that human salivary secretory leukocyte protease inhibitor (SLPI) inhibits HIV-1 by binding to a host cell surface protein of unknown identity. Using the yeast two-hybrid assay, we identified a gene sequence encoding a novel SLPI-binding protein (SLPI-BP). The 1.5-kb cDNA encodes a 318-amino acid protein with a predicted transmembrane segment near the C-terminus. Sequence analysis revealed that SLPI-BP is the human scramblase protein that is involved in the movement of membrane phospholipids. Co-expression of SLPI and SLPI-BP followed by an S-protein pulldown assay confirmed the specific interaction between these two proteins. Our data represent the first report for the identity of SLPI-BP.