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Solution structure of the apical stem-loop of the human hepatitis B virus encapsidation signal.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
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2006 (English)In: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 34, no 16, 4449-4457 p.Article in journal (Refereed) Published
Abstract [en]

Hepatitis B virus (HBV) replication is initiated by HBV RT binding to the highly conserved encapsidation signal, epsilon, at the 5' end of the RNA pregenome. Epsilon contains an apical stem-loop, whose residues are either totally conserved or show rare non-disruptive mutations. Here we present the structure of the apical stem-loop based on NOE, RDC and (1)H chemical shift NMR data. The (1)H chemical shifts proved to be crucial to define the loop conformation. The loop sequence 5'-CUGUGC-3' folds into a UGU triloop with a CG closing base pair and a bulged out C and hence forms a pseudo-triloop, a proposed protein recognition motif. In the UGU loop conformations most consistent with experimental data, the guanine nucleobase is located on the minor groove face and the two uracil bases on the major groove face. The underlying helix is disrupted by a conserved non-paired U bulge. This U bulge adopts multiple conformations, with the nucleobase being located either in the major groove or partially intercalated in the helix from the minor groove side, and bends the helical stem. The pseudo-triloop motif, together with the U bulge, may represent important anchor points for the initial recognition of epsilon by the viral RT.

Place, publisher, year, edition, pages
2006. Vol. 34, no 16, 4449-4457 p.
Keyword [en]
5' Untranslated Regions/chemistry, Hepatitis B virus/*genetics, Models; Molecular, Nuclear Magnetic Resonance; Biomolecular, Nucleic Acid Conformation, RNA; Viral/*chemistry, Solutions, Virus Replication
National Category
Medical and Health Sciences
URN: urn:nbn:se:umu:diva-6614DOI: 10.1093/nar/gkl582PubMedID: 16945960OAI: diva2:146283
Available from: 2007-12-16 Created: 2007-12-16 Last updated: 2010-04-19Bibliographically approved
In thesis
1. Structure and Dynamics of the Hepatitis B Virus Encapsidation Signal Revealed by NMR Spectroscopy
Open this publication in new window or tab >>Structure and Dynamics of the Hepatitis B Virus Encapsidation Signal Revealed by NMR Spectroscopy
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes the study of the three-dimensional structure and dynamics of the hepatitis B virus (HBV) encapsidation signal, epsilon, by means of nuclear magnetic resonance (NMR) and mutational data. HBV replicates by reverse transcription of an RNA pregenome into the viral DNA genome, which becomes enclosed in viral particles (encapsidation). Epsilon is a stem-loop structure within the RNA pregenome and both the primary sequence and secondary structure of epsilon are strongly conserved, in agreement with its essential function of propagating HBV. Epsilon is therefore a potential target for drug design. Studying the structure of epsilon requires development of new methods in the field of structural biology, as it is such a large RNA. Knowing the structure of epsilon will help to better understand the encapsidation mechanism and priming step of reverse transcription. This will help us in the search for antiviral drugs that block epsilon and prevent the viral reverse transcriptase from binding.

NMR spectroscopy is a method that provides detailed structural and dynamical data in solution under natural conditions. However, the size of the molecules that can be studied with NMR is limited. NMR spectra become more and more difficult to interpret as the size of the molecule increases. To circumvent this problem, large RNA molecules can be divided into smaller parts and only the parts essential for NMR studies are selected. The information obtained from these smaller fragments can then be used to determine the structure of the larger molecule. Furthermore, a new method of enzymatically synthesizing nucleoside triphosphates with isotopes suitable for NMR has made it possible to specifically label the RNA molecules. Using this method it is possible to derive highly detailed molecular structures of RNA up to a size of 150 nucleotides. The method of selective isotope labelling was applied to different parts of HBV epsilon. Three RNA fragments of 27 (apical loop), 36 (internal bulge) and 61 (whole epsilon) nucleotides (nt) were synthesized in the unlabelled form. The 27-nt and 36-nt RNAs were also synthesized with (13C, 15N, 1', 3', 4', 5', 5"-2H5)-labelled uridines. The 61-nt sequence was (13C, 15N)-guanidine labelled. This labelling allowed unambiguous assignment of otherwise inaccessible parameters. The unlabelled and labelled RNA sequences provided the necessary data for structure derivation of the whole epsilon.

The apical loop of epsilon forms a pseudo-triloop motif. There is only one conformation of the loop that fulfils all the restraints, including experimental chemical shifts. However, the loop adopts several structures that fulfil the experimental distance, torsion angle and residual dipolar coupling restraints. This may reflect true flexibility. Indeed, relaxation studies on the unlabelled and labelled 27-nt sequences show that the residues that show multiple conformations are flexible. This can be an important feature for the recognition and subsequent binding of epsilon to the viral polymerase.

The information gained on the HBV encapsidation signal is useful in our understanding of the initiation of replication of the virus. This can in turn contribute to the search for drugs against HBV.

Place, publisher, year, edition, pages
Umeå: Medicinsk biokemi och biofysik, 2004. 43 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 913
HBV, RNA, isotope labelling, NMR, structure determination
Research subject
Medical Biochemistry
urn:nbn:se:umu:diva-316 (URN)91-7305-719-3 (ISBN)
Public defence
2004-10-08, KB3A9, KBC, 13:00 (English)
Available from: 2004-09-16 Created: 2004-09-16 Last updated: 2010-04-12Bibliographically approved

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Flodell, SaraSchleucher, Jürgen
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