ADAMTSL-3/punctin-2, a novel glycoprotein in extracellular matrix related to the ADAMTS family of metalloproteases.

The complete primary structure of ADAMTSL-3/punctin-2, a novel member of the family designated ADAMTSL (a disintegrin-like and metalloprotease domain with thrombospondin type I motifs-like), was determined by cDNA cloning from a human placenta library. The predicted open reading frame encodes a protein of 1690 amino acids that has considerable similarity to ADAMTSL-1/punctin-1. These multi-domain proteins lack both a protease domain and a disintegrin-like domain but are remarkably similar in their domain organization to the ADAMTS proteases, hence the name ADAMTS-like. Punctin-2 contains thrombospondin type 1 repeats (TSRs), a cysteine-rich domain and a cysteine-free spacer domain in the precise order in which they occur in the ADAMTS proteases. However, the number and organization of the TSRs in punctin-2 is unique with respect to the ADAMTS proteases. Punctin-2 contains 13 TSRs arranged in two arrays separated by a region containing three immunoglobulin-like repeats. Northern blot analysis of RNA from human adult tissues demonstrated that ADAMTSL3 is widely expressed, with highest expression in liver, kidney, heart and skeletal muscle, whereas it is expressed at low levels in mouse embryos. We characterized two punctin-2 polyclonal antisera. Using these and a monoclonal antibody to a C-terminal myc tag, we show that in transfected COS-7 cells, punctin-2 is expressed as a 210-kDa glycoprotein that is located in the extracellular matrix. The domain structure of punctin-2 and its matrix localization suggest that it might play a role in cell-matrix interactions or in assembly of specific extracellular matrices.