Figure 1. Model of LON-2 parts that regulate DBL-1/TGF-β superfamily signaling. (A) The full-length LON-2 inhibits DBL-1 signaling and prevents a long body length phenotype. Full-length LON-2 (shown in A) remains functional if it lacks any one of the sequences containing RGD, all heparan sulfate attachment sites or the GPI anchor site. (B) The cylindrical N-terminal core protein, LON-2(1–368), requires the RGD motif for function. (C) The unstructured C-terminal 86 amino acid region, LON-2(423–508), requires both heparan sulfate attachment sites and a GPI anchor sequence to inhibit DBL-1 signaling. Arrows indicate parts required for function of the LON-2 variants shown in B and C. This diagram is based on tertiary structure predictions from the crystal structures of Dally-like and human GPC1.^17,18