Binds to the C-terminal propeptide of types I and II procollagens and may enhance the cleavage of that propeptide by BMP1. Interacts with heparin with high affinity, and type I or II collagen. Expressed at all stages of development, with expression level decreasing from 7 to 11 dpc and more abundant levels of expression at 15 and 17 dpc. First detectable at relatively low level at 10.5 dpc in the area of the third and fourth branchial arches. At 13.5 dpc easily discernible expression seems primarily confined to the cartilage primordia of future bones. At 15.5 dpc expressed at the highest levels in skeletal elements in the interior non-ossified regions of cartilaginous structures and excluded from regions of ossification. O-glycosylated; contains sialic acid.