Structural and functional insights into the human Upf1 helicase core.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Nonsense-mediated mRNA decay (NMD) is a crucial cellular surveillance pathway.
• Upf1p, a helicase superfamily 1 (SF1) protein, is central to NMD.
• Upf1p is proposed to use ATP hydrolysis for RNA-protein complex structural transitions.

Purpose of the Study:

• To elucidate the structural mechanisms of human Upf1p.
• To understand how ATP binding and hydrolysis regulate Upf1p function in NMD.

Main Methods:

• X-ray crystallography to determine the structure of human Upf1p catalytic core.
• Analysis of three nucleotide-bound states: phosphate, AMPPNP, and ADP.
• Structural comparison and mutational analysis.

Main Results:

• The crystal structure reveals two RecA-like domains and two additional protruding domains.
• A single-stranded RNA (ssRNA)-binding channel was identified.
• A cycle of conformational changes coupled to ATP binding/hydrolysis was elucidated.
• ATP binding was shown to destabilize ssRNA binding to Upf1p.

Conclusions:

• The conformational changes in Upf1p driven by ATP hydrolysis are key to its function in NMD.
• Structural insights provide a mechanism for how Upf1p regulates RNA binding during mRNA decay.