Basic Study
Copyright ©The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Virol. May 12, 2017; 6(2): 26-35
Published online May 12, 2017. doi: 10.5501/wjv.v6.i2.26
Structural and nucleic acid binding properties of hepatitis delta virus small antigen
Carolina Alves, Hong Cheng, João Paulo Tavanez, Ana Casaca, Severin Gudima, Heinrich Roder, Celso Cunha
Carolina Alves, João Paulo Tavanez, Ana Casaca, Celso Cunha, Global Health and Tropical Medicine, GHTM, Instituto de Higiene e Medicina Tropical, IHMT, Universidade Nova de Lisboa, 1349-008 Lisboa, Portugal
Hong Cheng, Heinrich Roder, Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA 19111, United States
Severin Gudima, Department of Microbiology, Molecular Genetics and Immunology, Kansas University Medical Center, Kansas City, KS 67874, United States
Author contributions: Alves C performed the majority of experiments; Cheng H performed the NMR and CD analysis; Casaca A performed production and purification of delta antigen; Tavanez JP, Gudima S and Roder H contributed to study design, provided critical discussions and wrote the manuscript; Cunha C designed and coordinated the research and wrote the manuscript.
Supported by Fundação para a Ciência e Tecnologia, FCT, to GHTM -UID/Multi/04413/2013; Carolina Alves and Ana Casaca were recipients of FCT PhD grants; João Paulo Tavanez is a recipient of a FCT post-doctoral fellowship SFRH/BPD/87494/2012.
Institutional review board statement: This study did not involve the use of any human and/or animal subjects.
Institutional animal care and use committee statement: This study did not involve the use of animal subjects.
Conflict-of-interest statement: The authors declare no conflicts of interest.
Data sharing statement: Technical appendix and dataset are available from the corresponding author at
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Celso Cunha, Associate Professor, Global Health and Tropical Medicine, GHTM, Instituto de Higiene e Medicina Tropical, IHMT, Universidade Nova de Lisboa, Rua da Junqueira 100, 1349-008 Lisboa, Portugal.
Telephone: +351-21-3652620 Fax: +351-21-3632105
Received: December 20, 2016
Peer-review started: December 25, 2016
First decision: January 16, 2017
Revised: February 8, 2017
Accepted: February 28, 2017
Article in press: March 2, 2017
Published online: May 12, 2017

To further characterize the structure and nucleic acid binding properties of the 195 amino acid small delta antigen, S-HDAg, a study was made of a truncated form of S-HDAg, comprising amino acids 61-195 (∆60HDAg), thus lacking the domain considered necessary for dimerization and higher order multimerization.


Circular dichroism, and nuclear magnetic resonance experiments were used to assess the structure of ∆60HDAg. Nucleic acid binding properties were investigated by gel retardation assays.


Results showed that the truncated ∆60HDAg protein is intrinsically disordered but compact, whereas the RNA binding domain, comprising residues 94-146, adopts a dynamic helical conformation. We also found that ∆60HDAg fails to multimerize but still contains nucleic acid binding activity, indicating that multimerization is not essential for nucleic acid binding. Moreover, in agreement with what has been previously reported for full-length protein, no apparent specificity was found for the truncated protein regarding nucleic acid binding.


Taken together these results allowed concluding that ∆60HDAg is intrinsically disordered but compact; ∆60HDAg is not a multimer but is still capable of nucleic acid binding albeit without apparent specificity.

Keywords: Hepatitis delta virus, Delta antigen, Nuclear magnetic resonance, Circular dichroism, Intrinsically disordered protein

Core tip: The characterization of a truncated form of S-HDAg lacking amino acids 1-60, ∆60HDAg is reported. Structure of ∆60HDAg was assessed by circular dichroism and nuclear magnetic resonance and its nucleic acid binding properties were investigated using gel retardation assays. This study demonstrates for the first time that ∆60HDAg is intrinsically disordered and a monomer. Furthermore, ∆60HDAg can bind a wide variety of nucleic acids without apparent specificity.