Co-crystal structure of HIV trans-activation response (TAR) RNA (rainbow ribbon) in complex with lab-evolved protein, TBP6.7 (blue Cα ribbon). A short peptide (pink) binds TAR outside the context of TBP6.7. (art by Joseph Wedekind). The underlying electron micrograph shows HIV virions (CDC image #13472 by Maureen Metcalfe and Tom Hodge).
Nucleic Acids Research Breakthrough article describes structure of HIV TAR complex with engineered binding protein and structure-based synthesis of antagonist
Investigators at multiple research institutes, led by Dr. Joseph Wedekind (University of Rochester) have described the high resolution crystal structure of a laboratory-evolved protein bound to its tightly associated HIV TAR RNA target, and subsequent synthesis and characterization of a stapled peptide mimic of the predominant RNA binding epitope in that protein. The study provided a detailed framework for peptide-mediated TAR recognition that might be generally applicable to target other disease-relevant RNAs.
HIV/AIDS is a global health threat that requires new insights into viral targets, especially those that resist mutation and promote novel aspects of the viral life cycle. In these respects, the HIV-1 trans-activation response (TAR) RNA is of ongoing interest. Previously, investigators (including some from this author group) developed methods to produce a unique lab-evolved protein ('TBP6.7') that recognizes TAR with extraordinarily high affinity compared to known TAR binders [Crawford et al. McNaughton (2016) ACS Chem. Biol. 8, 2206]. However, the molecular determinants of TAR recognition remained obscure, thus limiting the investigators' ability to further exploit that discovery. The crystal structure of this complex allowed investigators to determine that only a subset of the 'evolved' protein sequences are actually involved in RNA binding, with the preponderance of interactions localized to a short β-hairpin. This observation led them to synthesize a short, stapled peptide that mimics the β-hairpin and attenuates TAR-dependent transcription in HeLa nuclear lysate.
The study reported here [Belashov et al. Wedekind (2018) Nucleic Acids Res. 46, 6401-6415] is highly multi-disciplinary, spanning crystallography, site-directed mutagenesis, calorimetry, cell-surface display, ELISA, transcription assays, molecular dynamics simulations, and constrained peptide synthesis. In the end, the conversion of the parental RNA binding protein from single- to double-stranded RNA recognition implies that the protein has sufficient plasticity to recognize numerous RNA folds.
Reviewers and editors familiar with the work have stated that the study is "a strong contribution to a difficult field" that "will have substantial impact in the field of RNA recognition, ranging from applied (specifically targeting therapeutically relevant RNAs) to basic (understanding how RRMs bind to specific RNAs in the cell)"
The Wedekind laboratory at the University of Rochester investigates the mechanisms of action of non-protein-coding (nc)RNAs, and is interested especially in the three-dimensional architectures of these RNAs and how they bind to specific small molecules or peptides, leading to conformations that alter biological function. The research was supported by the University of Rochester Center for AIDS Research, and the National Institutes of Health.