EZRIN HAS PROPERTIES TO SELF-ASSOCIATE AT THE PLASMA-MEMBRANE

Ezrin, a member of a family of proteins involved in the interaction of the microfilament cytoskeleton with the plasma membrane, plays a role in membrane translocation in gastric parietal cells (Hanzel, D., Regg io, H., Bretscher, A., Forte, J. G. and Mangeat, P. (1991). EMBO J. 10 , 2363-2373). Human ezrin was expressed in and purified from Escherich ia coli. It possesses all the major biophysical, immunological and phy siological properties of natural ezrin. Upon microinjection in live ga stric HGT-1 cells, ezrin was incorporated into the dorsal microvilli, a site where the endogeneous protein is localized. By coimmunoprecipit ation and ezrin-affinity assays, two HGT-1 cell proteins of 77 and 72 kDa behaved as ezrin-binding proteins. In enriched gastric apical memb ranes, I-125-ezrin labelled proteins of 80, 77 and 72 kDa by overlay a ssay. The 80 kDa protein was identified as ezrin and the 77 and 72 kDa proteins as gastric forms of proteins structurally related to ezrin, such as radixin and moesin. In insect cells infected with a recombinan t baculovirus, one-third of overexpressed ezrin accumulated at the pla sma membrane. Ezrin bound a 77 kDa endogenous peripheral membrane prot ein, behaving as an insect counterpart of the mammalian ezrin family. In addition to the respective role of the amino- and carboxyl-terminal domains of ezrin in linking the membrane and the cytoskeleton (Algrai n, M., Turunen, O., Vaheri, A., Louvard, D. and Arpin, M. (1993). J. C ell Biol. 120, 129-139), both domains interacted synergistically in a salt-dependent manner to trigger self-association of ezrin. Ezrin's se lf-association properties could represent another way of regulating th e number of ezrin molecules bound at specific membrane sites.