Collagens are the most abundant family of extra cellular matrix (ECM) proteins, accounting for two-thirds of the dry mass of adult articular cartilage. Several subtypes have been identified including types II, IX, X, XI, VI, XII, and XIV collagen, however 80 – 90% of the collagen in the body consists of types I, II, and III. Collagen is a long thin protein which consists of three coiled subunits: two α1(I) chains and one α2(I). Type 1 collagen forms part of the major structure of the bone, and mutations in the α1(I) or α2(I) genes lead to osteogenesis imperfecta, or brittle-bone disease.

Collagen is cleaved by mammalian tolloid (mTld) and its splice variant; bone morphogenetic protein 1 (BMP1), a metalloprotease and member of the peptidase M12A family enzymes.

This peptide contains a FRET (fluorescence or Förster resonance energy transfer) pair. N-terminal 5-Carboxyfluorescein (5-FAM), a widely used green fluorescent tag which excites at 495 nm and emits at 517  nm, and a 5-Carboxytetramethylrhodamine (5-TAMRA), present on the side chain of a C-terminal lysine which has been added to the peptide. 5-TAMRA is a widely used fluorescent dye which excites at 546 nm and emits at 579 nm. In the intact peptide TAMRA quenches the fluorescence of 5-FAM, however upon cleavage of the peptide by a protease such as BMP1, the fluorescence of 5-FAM is recovered and can be monitored.