This is the N-terminal domain of human fibrillin-1. Fibrillin is a primary constituent of microfibrils in the extracellular matrix of many elastic and non-elastic connective tissues. This domain, known as the fibrillin unique N-terminal (FUN) domain, constitutes the minimal interaction site for the fibrillin C terminus. The FUN domain has homologs in the human proteins LTBP-1L/2 and VWCE, which are also associated with a C-terminal EGF-like domain [1].

1: Structure of the fibrillin-1 N-terminal domains suggests that heparan sulfate regulates the early stages of microfibril assembly. Yadin DA, Robertson IB, McNaught-Davis J, Evans P, Stoddart D, Handford PA, Jensen SA, Redfield C; Structure. 2013;21:1743-1756. PMID:24035709