Re. Ward et al., A CONSERVED FUNCTIONAL DOMAIN OF DROSOPHILA CORACLE IS REQUIRED FOR LOCALIZATION AT THE SEPTATE JUNCTION AND HAS MEMBRANE-ORGANIZING ACTIVITY, The Journal of cell biology, 140(6), 1998, pp. 1463-1473
The protein 4.1 superfamily is comprised of a diverse group of cytopla
smic proteins, many of which have been shown to associate with the pla
sma membrane via binding to specific transmembrane proteins, Coracle,
a Drosophila protein 4.1 homologue, is required during embryogenesis a
nd is localized to the cytoplasmic face of the septate junction in epi
thelial cells, Using in vitro mutagenesis, we demonstrate that the ami
no-terminal 383 amino acids of Coracle define a functional domain that
is both necessary and sufficient for proper septate junction localiza
tion in transgenic embryos, Genetic mutations within this domain disru
pt the subcellular localization of Coracle and severely affect its gen
etic function, indicating that correct subcellular localization is ess
ential for Coracle function. Furthermore, the localization of Coracle
and the transmembrane protein Neurexin to the septate junction display
an interdependent relationship, suggesting that Coracle and Neurexin
interact with one another at the cytoplasmic face of the septate junct
ion. Consistent with this notion, immunoprecipitation and in vitro bin
ding studies demonstrate that the amino-terminal 383 amino acids of Co
racle and cytoplasmic domain of Neurexin interact directly. Together t
hese results indicate that Coracle provides essential membrane-organiz
ing functions at the septate junction, and that these functions are ca
rried out by an amino-terminal domain that is conserved in all protein
4.1 superfamily members.