The CEACAM1 N-terminal Ig domain mediates cis- and trans-binding and is essential for allosteric rearrangements of CEACAM1 microclusters

Klaile, Esther; Vorontsova, Olga; Sigmundsson, Kristmundur; Müller, Mario M.; Singer, Bernhard B.; Öfverstedt, Lars-Göran; Svensson, Stina; Skoglund, Ulf; Öbrink, Björn

Tissue structure, cellular behavior, and cell function are regulated by homotypic and heterotypic intercellular interactions mediated by cell adhesion molecules (CAMs) . Knowledge about CAM-mediated transmembrane signaling has medical implications because it will allow tailored design of therapeutic agents that can target specific CAMs. For a large number of CAMs, the molecular/biochemical properties are known in great detail, and crystal structures have been reported for many CAM ectodomains (Xiong et al., 2001; Boggon et al., 2002; Tan et al., 2002; Soroka et al., 2003; Xiao et al., 2004; Fedarovich et al., 2006; Korotkova et al., 2008) . However, with the exception of some integrins (Kim et al., 2003; Takagi et al., 2003; Xiao et al., 2004 ), this has not yet given satisfactory explanations for mechanisms of ectodomain-initiated signal generation. Signaling by singlepass CAMs belonging to the immunoglobulin superfamily remains a mystery and requires additional information on the structural dynamics and supramolecular organization of native CAMs at the cell surface and how these properties are influenced by homophilic and heterophilic CAM interactions. To achieve this goal, x-ray crystallography has to be complemented by other methods that give information on individual molecules in large populations.