Key result
The HERV-K/HML-2 export adapter protein Rec forms stable tetramers that bind to the complex folded structure of the RcRE pck30 RNA, with up to three Rec tetramers binding preferentially to purine-rich motifs.
The HERV-K Rec protein forms stable tetramers that bind to the complex folded structure of the RcRE, with binding tightened by purine-rich motifs to facilitate viral RNA export.
Preclinical findings only; leaves open whether Rec tetramers represent antiviral targets in humans.
The RNA export adaptor protein Rec, encoded for by the human endogenous retrovirus HERV-K/HML-2 elements, binds to the Rec responsive element (RcRE) located in the 3' untranslated region of HERV-K/HML-2 transcripts. Binding allows the nucleocytoplasmic export of unspliced viral RNA, thereby overcoming host restriction. Chemical probing of the secondary structure of the RcRE corroborated the theory that the RcRE forms a complex folded structure with seven stem-loop regions. Laser-induced liquid beam ion desorption mass spectrometry revealed that Rec forms stable tetramers, which are further stabilized upon RNA binding. The RNA protein complex consists of three Rec tetramers, which bind to multiple sites on the RcRE-preferentially to purine-rich motifs-which represent several low-affinity binding sites. Mutated RcREs, with one to three purine-rich motifs deleted, were still bound and exported by Rec, indicating that the complex folded structure of the RcRE is important for Rec binding. This suggests a binding model where up to three Rec tetramers bind to the complex folded structure of the RcRE and the binding seems to be tightened by recognition of the purine-rich motifs.
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Langner et al. (2012) studied this question. Rec protein and RcRE pck30 RNA was evaluated on Binding affinity and stoichiometry. The HERV-K/HML-2 export adapter protein Rec forms stable tetramers that bind to the complex folded structure of the RcRE pck30 RNA, with up to three Rec tetramers binding preferentially to purine-rich motifs.
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