Microfibrils are composed largely of fibrillin but also contain covalently-linked microfibril associated glycoproteins MAGP-1 (MFAP2) and MAGP-2 (MFAP5). MFAP2 is a structural component of almost all vertebrate microfibrils (Gibson et al. 1989, Trask et al. 2000, Jensen et al. 2001). It appears to be important for tissue development and/or homeostasis, including regulation of bone remodelling and deposition of tissue fat (Weinbaum et al. 2008). The C-terminal half of MFAP2 is rich in cysteines and contains a matrix-binding domain that facilitates interactions with fibrillin (Weinbaum et al. 2008). The related MFAP5 similarly binds to microfibrils (Gibson et al. 1998) but with a restricted expression profile.