Functional analyses identify the L1 ORF2p Cryptic domain as a hub for intramolecular interfaces required for...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Long Interspersed Element-1 (L1) retrotransposition is crucial for genome dynamics.
• The L1 ORF2p protein harbors endonuclease (EN) and reverse transcriptase (RT) domains essential for retrotransposition.
• The ORF2p Cryptic region, lacking known homologues, is conserved and vital for L1 retrotransposition via an unknown mechanism.

Purpose of the Study:

• To elucidate the functional role of intramolecular interactions involving the L1 ORF2p Cryptic region in retrotransposition.
• To investigate the impact of Cryptic domain interactions with EN, RT, and C-terminal domains (CTD) on L1 activity and toxicity.

Main Methods:

• Site-directed mutagenesis to disrupt Cryptic interactions.
• Co-immunoprecipitation assays to assess protein complex formation.
• In vitro assays for cDNA synthesis and RNA binding.
• Functional retrotransposition assays.
• Cytotoxicity assays.
• Molecular modeling analyses.

Main Results:

• The Cryptic region acts as an independent domain, rescuing cDNA synthesis in trans.
• The Cryptic:RT interface is critical for cDNA initiation/elongation and potentially EN function, while reducing ORF2p toxicity.
• The Cryptic:CTD interface influences retrotransposition and increases ORF2p toxicity, but is not essential for initial cDNA synthesis.

Conclusions:

• Intramolecular interactions involving the Cryptic domain are indispensable for multiple stages of L1 retrotransposition.
• The Cryptic region functions as a nonenzymatic structural domain.
• Targeting the Cryptic domain offers a potential therapeutic strategy for cancers with elevated L1 expression.