Domain organization within the nuclear export factor Mex67:Mtr2 generates an extended mRNA binding surface

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• The Mex67:Mtr2 complex is the primary yeast nuclear export factor for bulk mRNA and ribosomal subunits.
• Mex67, a modular protein, possesses RRM, LRR, NTF2-like, and UBA domains, traditionally viewed as flexibly linked.
• Existing models propose RRM/LRR domains bind RNA, while NTF2-like/UBA domains interact with FG-nucleoporins for nuclear pore translocation.

Purpose of the Study:

• To investigate the role of the NTF2-like domain in RNA binding within the Mex67:Mtr2 complex.
• To elucidate the structural organization and domain dynamics of the Mex67:Mtr2 complex.
• To understand how the complex's structure facilitates both RNA binding and nuclear pore passage.

Main Methods:

• X-ray crystallography to determine the 3.3 Å resolution structure of the Mex67(ΔUBA):Mtr2 complex.
• Small-angle X-ray scattering (SAXS) to complement structural data and assess domain mobility.
• Biochemical assays to analyze RNA-binding capabilities of different domains.

Main Results:

• The NTF2-like domain of Saccharomyces cerevisiae Mex67:Mtr2 contributes to RNA binding.
• Structural data revealed a defined spatial arrangement between the LRR and Mex67(NTF2L):Mtr2 regions, with RRM and UBA domains exhibiting greater mobility.
• A continuous RNA-binding interface, formed by clusters of positively-charged residues on the LRR and NTF2-like domains, is positioned opposite to the FG-nucleoporin interaction site.

Conclusions:

• The NTF2-like domain plays a dual role in RNA binding and potentially FG-nucleoporin interaction.
• The Mex67:Mtr2 complex exhibits a specific conformation that spatially separates RNA binding and nuclear pore interaction surfaces.
• This structural organization is critical for efficient mRNA and ribosomal subunit nuclear export.