Journal of Virology, July 2008, p. 6787, Vol. 82, No. 14
0022-538X/08/$08.00+0 doi:10.1128/JVI.01084-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
| SPOTLIGHT |
Articles of Significant Interest Selected from This Issue by the Editors
A Retrovirus Assembly Domain that Affects Virion MorphologyThe retroviral Gag protein assembles into spherical, immature virions. Proteolytic cleavage of Gag then leads to a structural reorganization called maturation. In the Gag proteins of human immunodeficiency virus type 1 and Rous sarcoma virus (RSV), a spacer peptide (SP) separates the CA and NC domains. Keller et al. (p. 6788-6797) now have defined a 24-amino-acid assembly domain in RSV Gag that includes the SP and adjoining sequences in CA and NC. Mutational disruption of this domain leads to budding of long tubular particles. Thus, the SP assembly domain acts as a molecular switch, promoting formation of the immature Gag lattice.
Monitoring Human Immunodeficiency Virus Type 1 Early Fusion Dynamics One Molecule at a Time
Human immunodeficiency virus type 1 (HIV-1) attachment to host cells is governed by dynamic binding interactions between viral gp120 and host-cell receptor CD4 and a chemokine coreceptor such as CCR5. Dobrowsky et al. (p. 7022-7033) measured the binding of HIV-1 virions to its receptors by molecular-force spectroscopy at single-molecule resolution. These measurements highlight the instability of gp120-receptor bonds, uncover a synergistic role for coreceptor CCR5 in the progression of the gp120-CD4 bond, and suggest that the virus-cell adhesion complex is functionally arranged around a long-lived gp120-coreceptor bond.
Targeting of APOBEC3G into Replication-Competent Hepatitis B Virus Nucleocapsids
The cytidine deaminase APOBEC3G (A3G) is a powerful intrinsic antiviral immunity factor. A3G antiviral function depends on its incorporation into assembling viral particles via a poorly understood mechanism. Nguyen and Hu (p. 6852-6861) now show that the incorporation of A3G into the pararetrovirus hepatitis B virus (HBV) depends on specific interactions with the viral reverse transcriptase (RT) and the viral RNA packaging signal 
. Thus, A3G is specifically targeted to replication-competent HBV nucleocapsids and not "empty" capsids without RT or viral RNA, in stark contrast to conventional retroviruses that package A3G without RT or viral RNA.
The CD4 Response to Vaccinia Virus Is Very Diverse
Vaccinia virus (VV) stimulates highly effective immune responses. CD4+ T cells are indirectly required for production of antiviral antibodies and effective CD8+ T-cell memory. Jing et al. (p. 7120-7134) used a novel whole-proteome technology to show that the human CD4+ T-cell response to VV is remarkably broad, targeting an average of 39 open reading frames per person. Immunodominant proteins are mainly abundant virion proteins that partially overlap prevalent VV antibody targets. The T-cell responses to replication-competent VV may provide a benchmark for judging the efficacy of replication-incompetent vaccines and VV vectors.
Structural Studies Reveal Molecular Mechanisms of Cross-Species Infections by Severe Acute Respiratory Syndrome Coronavirus
The severe acute respiratory syndrome coronavirus (SARS-CoV) is thought to have crossed a species barrier from palm civets to humans to produce the SARS epidemic in 2002 to 2003. How this occurred is unknown. Li (p. 6984-6991) analyzed the crystal structures of interfaces between SARS-CoV and its host receptor. This work reveals that SARS-CoV underwent stepwise mutations to eliminate imbalanced salt bridges at the virus-receptor interface. These mutations allowed the virus to gain infectivity for human cells.
Journal of Virology, July 2008, p. 6787, Vol. 82, No. 14
0022-538X/08/$08.00+0 doi:10.1128/JVI.01084-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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