Homodimer. Binds to heparin and chondroitin sulfate E. Expressed in lung, eye, testis, uterus, ovary, and to a lesser extent in heart, skeletal muscle, mammary gland, skin and prostate. Within the eye, mainly present in photoreceptor layers (at protein level). Seems to be cleaved at Lys-301 after secretion. O-glycosylated but not N-glycosylated.