Key regulator of the Wnt signaling pathway that mediates lipid modification of Wnt proteins. Acts as a protein-serine O-palmitoleoyltransferase that catalyzes the attachment of palmitoleate, a 16-carbon monounsaturated fatty acid (C16:1), to Wnt proteins. Serine palmitoleylation of WNT proteins is required for efficient binding to frizzled receptors. Has a role in cell specification, specifically in blastomere signaling. Involved in cytosketetal polarity. Required for the orientation of mitotic spindle axis. (9Z)-hexadecenoyl-CoA + [Wnt protein]-L-serine = [Wnt protein]-O-(9Z)-hexadecenoyl-L-serine + CoA Belongs to the membrane-bound acyltransferase family. Porcupine subfamily.