Lipid modification of secreted signaling proteins. Hui Hua Liu¹, Rayshonda Hardy², Steven Blais¹, Thomas Neubert¹, Marilyn Resh², Jessica Treisman¹. 1) Kimmel Center for Biology and Medicine of the Skirball Institute, NYU School of Medicine, New York, NY; 2) Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY.

   Lipid modification of secreted proteins can modulate their trafficking, secretion, diffusion, or ability to bind and activate their receptors. Three signaling ligands of different families have been found to acquire lipid modifications that regulate their fates and functions. Hedgehog and Spitz are both palmitoylated on their N-terminal cysteine residues by the acyltransferase Rasp; we have shown that the recognition sequence for Rasp and its mammalian homologue Hhat lies within the first 10 amino acids of these proteins. A related acyltransferase, Porcupine, transfers two fatty acids to Wnt family members. We are investigating whether additional signaling proteins in different families can also be lipid modified. We expressed a set of secreted proteins in cultured cells and screened them for hydrophobicity using a detergent extraction assay. This screen identified members of the BMP and Activin families as potential candidates for lipid modification. We are focusing on Glass bottom boat (Gbb), a BMP7 homologue important for wing patterning, synapse growth and energy homeostasis. Both full-length Gbb and its mature secreted form appear more hydrophobic than predicted from their amino acid sequence. We are using mass spectrometric analysis of Gbb purified from a stable cell line to look for lipid modifications and identify their attachment sites.