Abstract

The Ca²⁺ -dependent membrane-spanning classical cadherins bind directly to cytosolic catenins. This cadherin–catenin interaction is known to be critical for the fundamental role of cadherins in cell–cell adhesion. The small subfamily of the 7D-cadherins, however, cannot interact with catenins due to their highly truncated cytoplasmic tail. Thus far, no cytoplasmicinteractionpartner for the 7D-cadherins has been described.

With the use of the cytoplasmic domain of the Ksp (kidney-specific)-cadherin, which belongs to the family of 7D-cadherins, as bait in affinity chromatography with human kidney lysates, the small heat-shock protein aB-crystallin was identified by matrix-assisted laser desorption/ionization–time-of-flight analysis as a cytosolic binding partner of Ksp-cadherin. This interaction was verified by co-immunoprecipitation analysis.With the use of overlapping peptides representing the entire aB-crystallin molecule, the N-terminal part of aB-crystallin, which does not possess chaperone activity, was identified as responsible for the binding to Ksp-cadherin.

This interaction was found to be specific since only the cytoplasmic domain of Ksp-cadherin, but not LI (liver–intestine)-cadherin (another member of the 7D-cadherin family), interacted with aB-crystallin. In the human kidney, both aB-crystallin and Ksp-cadherin co-localize to cells of the collecting duct. They also co-localize with the actin cytoskeleton and co-precipitate with the latter. These findings suggest that the interaction of Ksp-cadherin with aB-crystallin is important for the connection of Ksp-cadherin to the cytoskeleton and thus for maintaining tissue integrity in the kidney.