Figure 1. Modular structure of perlecan chain depicted as train cars assembled in tandem behind a common “engine” that is unique to perlecan.

The individual modules are self-folding, joined by linker sequences between. The locomotive depicts the signal sequence driving the train into the cellular secretory path for secretion into the extracellular space. The SEA module is envisioned as the coal car, and is near the region where the majority of the glycosylation occurs in domain I (sugars not shown). Features of note include the “split cars” such as the three laminin EGF-like modules split by a laminin IV type A-like module (red split by blue). Note the one Ig-like module at the end of domain II, with the rest in long domain IV. The curvature of the train is suggested by the visualization of the perlecan monomer by atomic force microscopy (see text).