Microdomains

One sorting mechanism of apical and basolateral proteins in epithelial cells is based on their solubility profiles with Triton X-100. Nevertheless, as our group could show, apical proteins themselves are also segregated beyond the trans-Golgi network by virtue of their association or non-association with cholesterol- and sphingolipid-rich microdomains. Therefore, extractability with Triton X-100 does not constitute an absolute criterion of protein sorting.

Therefore we investigated the solubility patterns of apical and basolateral proteins with other detergents and demonstrated that the mild detergent Tween 20 is adequate to discriminate between apical and basolateral proteins during early stages in their biosynthesis. This suggests an early polarized sorting mechanism prior to maturation in the Golgi apparatus.

For the early as well as the late secretory pathways, our current focus is the functional characterization of membrane components related to detergent-resistant microdomains.