Clathrin-mediated endocytosis
Clathrin-mediated endocytosis is a process by which
virtually all eukaryotic cells internalize nutrients, antigens, growth
factors, pathogens and recycling receptors (Takei & Haucke, 2001).
Internalization may occur either constitutively or in response to certain stimuli
such as in the recycling of synaptic vesicles after exocytosis (Galli & Haucke, 2001).
The basic mechanisms underlying endocytosis have fascinated cell biologists for more than two decades,
but it has become clear only recently how
clathrin-coated vesicle budding from the plasma membrane is
initiated at the molecular level (fig. 1).
Figure 1: Clathrin-coated vesicle formation and disassembly regulates receptor recycling or degradation; courtesy of Dr.
Helge Gad, Karolinska Institute, Stockholm)
We are interested in determining the exact function of adaptor molecules such as
AP-2 in the regulation of clathrin-coated pit assembly and cargo protein sorting.
Recent work from us and others has shown that PI(4,5)P2 plays pivotal roles in membrane recruitment via directly binding to AP-2
(Rohde et al., 2002) as well as other adaptor proteins and accessory molecules. During initial assembly of
clathrin-coated pits a 'dual-key'
strategy is used that relies on interactions of AP-2
with PI(4,5)P2 and with transmembrane cargo proteins (fig. 2).
Figure 2: 'Dual-key strategy' used by adaptor proteins for membrane recruitment;
taken from Wenk & De Camilli, 2004)
We have identified stonins as novel adaptor proteins that serve to couple
internalization of presynaptic membrane proteins including synaptotagmin with AP-2 at
endocytic sites (Walther et al., 2001; 2004; fig. 3).
Figure 3: Colocalization of transfected EGFP-stonin 2 and synaptotagmin
I at presynaptic sites in cultured primary neurons; taken from Walther et al., 2004)
To investigate the function of clathrin and adaptor molecules in endocytotic vesicle
cycling we are using a combination of biochemical, cell biological, and genetic tools.
We are also developing molecular and genetic tools to specifically inhibit
clathrin-mediated endocytosis at distinct steps of its cycle (fig.1) in order
to investigate the physiological consequences of impaired membrane trafficking.
Much of this work is performed together with a number of collaborating labs in the
US, England, Israel, and Germany.
Last update: Nov, 2005 by Claus Rodemer
