Functions together with adgra2 to enable brain endothelial cells to selectively respond to Wnt7 signals (wnt7a or wnt7b) (PubMed:26051822, PubMed:26657775). Plays a key role in Wnt7-specific responses: required for central nervous system (CNS) angiogenesis and blood-brain barrier regulation (PubMed:26051822, PubMed:26657775). Acts as a Wnt7-specific coactivator of canonical Wnt signaling by decoding Wnt ligands: acts by interacting specifically with the disordered linker region of Wnt7, thereby conferring ligand selectivity for Wnt7. Adgra2 is then required to deliver reck-bound Wnt7 to frizzled by assembling a higher-order RECK-ADGRA2-Fzd-LRP5-LRP6 complex. Also acts as a serine protease inhibitor (By similarity). Interacts (via knot repeats) with wnt7a (via disordered linker region); the interaction is direct (By similarity). Interacts (via knot repeats) with wnt7b (via disordered linker region); the interaction is direct (By similarity). Interacts with adgra2; the interaction is direct (PubMed:26051822). Colocalizes with adgra2 at the plasma membrane. Expressed in the cerebral endothelium. The Kazal-like domains mediate the serine protease inhibitor activity. Belongs to the RECK family.