Figure 1:

Topological model of ABCA4 showing the organization of the domains and the location of the missense mutations analyzed in this study. ECD1 and ECD2 – exocytoplasmic domains 1 and 2; TMD1 and TMD2 – transmembrane domains 1 and 2. The 12 transmembrane segments are numbered. NBD1 and NBD2 – nucleotide binding domains 1 and 2. Green – proposed intracellular α-helices (IH); two short hairpin α-helices between membrane spanning segments 5 and 6 and 11 and 12 are shown. The missense mutations are colored to indicate their severity class as defined in this study (see Table I) with Class 1 (severe) in red; Class 2 (moderate) in blue; and Class 3 (mild) in grey.