Enhancement of the thermostability of mouse claudin-3 on complex formation with the carboxyl-terminal region of Clostridium perfringens enterotoxin improves crystal quality

Tight junctions regulate substance permeation through intercellular spaces as a physical barrier or a paracellular pathway, and play an important role in maintaining the internal environment. Claudins, which are tetraspan-transmem-brane proteins, are pivotal components of tight junctions. In mammals 27 claudin subtypes have been identified, each of which interacts with specific subtypes. Although the crystal structures of several subtypes have been determined, the molecular mechanisms underlying subtype specificity remain unclear. Here, mouse claudin-3 (mCldn3) was crystallized in complex with the C-terminal region of Clostridium perfringens enterotoxin (C-CPE) for the structural analysis of an additional claudin subtype. mCldn3 alone was difficult to crystallize, but complex formation with C-CPE enhanced the thermostability of mCldn3 and facilitated its crystallization. The introduction of an S313A mutation into C-CPE further improved its thermostability, and the resolution limits of the diffraction data sets improved from 8 angstrom for the wild-type complex to 4.7 angstrom for the S313A mutant complex.