Molecular organisation of intercellular adhesion junctions by cryo-electron tomography of vitreous sections
Authors: Al-Amoudi Ashraf 
Published: November 2013

Ashraf Al-Amoudi1,2 and Achilleas Frangakis3 1Center of Advanced European Studies and Research (caesar), Department of Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany, 2German Center of Neurodegenerative Diseases, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany 3Goethe Universität - Institut für Biophysik Max-von-Laue-Str. 1 60438 Frankfurt, Germany Intercellular adhesion junctions are fundamental for the function and development of multi-cellular organisms. They are widely distributed in animal tissues and most abundant in tissues that are subjected to considerable mechanical stress such as heart, skin and muscle. Desmosomes and adherens junctions (AJs) represent major categories of these junctions. The intercellular space of desmosomes and AJs relies on the associations between members of Ca2+- dependent adhesion molecules called cadherins which share high sequence similarity among them.The intracellular region of the junctions form distinct plaque on the cytoplasmic face of the plasma membrane and form complex network of molecular interactions that link the extracellular region of cadherins with the cytoskeleton. Disruption of cadherins or plaques is the hallmark of many blistering and cancer diseases. Recently, the first crystal structure of the full extracellular domains of C-cadherin (a representative of classical cadherins) showed that the cadherin molecules adopt a stable, curved conformation1. In this crystal structure, the neighbouring molecules are oriented in antiparallel and engaged through a mutual exchange of the tryptophan 2 (Trp2) forming a W-like shape. Such Trp2 trans-interactions were supported by mutagenesis data and cell-adhesion assays and are now considered to be physiologically relevant2. Recently, using cryo-electron tomography and quantitative analysis by sub-tomogram averaging, we revealed the molecular organization of desmosomal cadherins and plaque3,4. Our results show two predominant cis- and trans- interactions alternating in a periodic manner similar to the arrangements observed in the linear zipper of the crystal structure of N-cadherins5. In addition, the resulting molecular model explains previous two dimensional images observed with CEMOVIS at various orientations and yields important insights into the assembly of cadherin-based intercellular junction. Our analysis of the desmosomal plaque revealed two-dimensional interconnected quasiperiodic lattice with similar spatial orgnaization of the extracellular region of the desmosome5. We are currently studying the molecular organization of AJs from mouse intestine. Our results indicate highly-organized structure of E-cadherin compatible with the X-ray structure of classical cadherins1. All these results will be presented in the conference. 1. T.J. Boggon, J. Murray, S. Chappuis-Flam ent, E. Wong, B.M. Gumbiner and L. Shapiro, Science. 296 (2002) 1308. 2. S. Troyanovsky, Eur J Cell Biol 84 (2005), 225. 3. A. Al-Amoudi, D. C. Díez, M. Betts, A. S. Frangakis, Nature 450 (2007), 832. 4. A. Al-Amoudi, D. Castaño-Diez, D. P. Devos, R.B. Russell, G.T. Johnson, A. S. Frangakis,Proc. Natl. Acad. Sci. 108 (2011), 6480. 5. L. Shapiro, A.M. Fannon, P.D. Kwong, A. Thompson, M.S. Lehmann,G. Grubel, J.F. Legrand, J. Als-Nielsen, D.R. Colman and W.A. Hendrickson, Nature. 374 (1995) 327.