Increased GTP-binding to dynamin II does not stimulate receptor-mediated endocytosis

Regarding the molecular mechanism of dynamin in receptor-mediated endocytos is, GTPase activity of dynamin has been thought to have a critical role in endocytic vesicle internalization. However, a recent report suggested that GTP-binding to dynamin itself activates the dynamin to recruit molecular ma chinery necessary for endocytosis. In this study, to investigate the role o f GTP binding to dynamin II, we generated two mutant dynamin II constructs: G38V and K44E, G38V, its GTP binding site might be mainly occupied by GTP caused by reduced GTPase activity, and K44E mutant, its GTP binding site mi ght be vacant, caused by its decreased affinity for GTP and GDP. From the a nalysis of the ratio of GTP vs GDP bound to dynamin, we confirmed these pro perties. To test the effect of these mutant dynamins on endocytosis, we per formed flow cytometry and confocal immunofluorescence analysis and found th at these two mutants have inhibitory effect on transferrin-induced endocyto sis. Whereas fluorescent transferrin was completely internalized in wild-ty pe (WT), dynamin II expressing cells, no intracellular accumulation of fluo rescent transferrin was found in the cells overexpressing K44E and G38V mut ant. Interestingly, the amount of GTP bound to K44E was increased when endo cytosis was induced than that bound to WT. The present results suggested th at the GTPase activity of dynamin II is required for formation of endocytic vesicle and GTP-binding to dynamin II per se is not sufficient for stimula ting endocytosis. (C) 2001 Academic Press.