Structural bases for tetraspanin functions

Abstract

The tetraspanin transmembrane glycoproteins are considered as “molecular facilitators” which simultaneously interact with, and thereby bring into close proximity specific proteins involved in cellular activation and transduction processes. Elucidation of the 3D structure of tetraspanins is an essential step in understanding of their facilitator function and of the molecular basis of their partner specificity. Although there are currently no experimental atomic resolution structures of a whole tetraspanin molecule, recent information gained from three different approaches has led to a rather comprehensive picture of the structural organization of tetraspanins. These include: (1) crystallographic structures of the main extracellular domain of the ubiquitous tetraspanin CD81; (2) a 6 Å-resolution cryo-EM structure of the tetraspanins uroplakin UPIa and UPIb in the urothelial plaque of mammalian urothelium; (3) molecular modeled-structures of the complete CD81 tetraspanin. On the basis of such structural data, a qualitative view of tetraspanin structure-function relationship is emerging, including a delineation of regions of the molecule involved in specific interactions with partners, as well as an understanding of the structural basis of the multilevel partner specificity of tetraspanins and of the tetraspanin network organization.