Insights into the low adhesive capacity of human T-cadherin from the NMR structure of Its N-terminal extracellular domain.
T-cadherin is unique among the family of type I cadherins, because it lacks transmembrane and cytosolic domains, and attaches to the membrane via a glycophosphoinositol anchor. The N-terminal cadherin repeat of T-cadherin (Tcad1) is approximately 30% identical to E-, N-, and other classical cadherins. However, it lacks many amino acids crucial for their adhesive function of classical cadherins. Among others, Trp-2, which is the key residue forming the canonical strand-exchange dimer, is replaced by an isoleucine. Here, we report the NMR structure of the first cadherin repeat of T-cadherin (Tcad1). Tcad1, as other cadherin domains, adopts a beta-barrel structure with a Greek key folding topology. However, Tcad1 is monomeric in the absence and presence of calcium. Accordingly, lle-2 binds into a hydrophobic pocket on the same protomer and participates in an N-terminal beta-sheet. Specific amino acid replacements compared to classical cadherins reduce the size of the binding pocket for residue 2 and alter the backbone conformation and flexibility around residues 5 and 15 as well as many electrostatic interactions. These modifications apparently stabilize the monomeric form and make it less susceptible to a conformational switch upon calcium binding. The absence of a tendency for homoassociation observed by NMR is consistent with electron microscopy and solid-phase binding data of the full T-cadherin ectodomain (Tcad1-5). The apparent low adhesiveness of T-cadherin suggests that it is likely to be involved in reversible and dynamic cellular adhesion-deadhesion processes, which are consistent with its role in cell growth and migration.
Dames
Sonja A
SA
Department of Structural Biology, University of Basel, Klingelbergstr. 70, 4056 Basel, Switzerland. sonja.dames@unibas.ch
Bang
Eunjung
E
Haüssinger
Daniel
D
Ahrens
Thomas
T
Engel
Jürgen
J
Grzesiek
Stephan
S
D000595:Amino Acid Sequence; D015820:Cadherins / Q000737:chemistry*; D002448:Cell Adhesion; D004247:DNA / Q000737:chemistry; D006801:Humans; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008854:Microscopy, Electron; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
D015820:Cadherins; C099972:H-cadherin; D008024:Ligands; D004247:DNA