Structure of the C-terminal FG-nucleoporin binding domain of Tap/NXF1.

The vertebrate Tap protein is a member of the NXF family of shuttling transport receptors for nuclear export of mRNA. Tap has a modular structure, and its most C-terminal domain is important for binding to FG repeat-containing nuclear pore proteins (FG-nucleoporins) and is sufficient to mediate nuclear shuttling. We report the solution structure of this C-terminal domain, which is based on a distinctive arrangement of four alpha-helices and is joined to the next module by a flexible 12-residue Pro-rich linker. F617A Tap suppresses FG-nucleoporin binding by the most C-terminal domain that, together with the structure of the other modules from which Tap is constructed, provides a structural context for its nuclear shuttling function.