Crystal Structure of Vaccinia Viral A27 Protein Reveals a Novel Structure Critical for Its Function and Complex Formation with A26 Protein

PLoS Pathogens

Shu-Jung Chang¹  Cheng-Tse Lin²  Andrew H. J. Wang²  Tao-Hsin Chang³  Iren Wang³  Shang-Te Danny Hsu³  Wen Chang³  Meng-Ru Ho³  Tzu-Ping Ko³  Rey-Ting Guo³  Fu-Lien Hsieh⁴ 

[1] Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan;Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan;Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan;Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan

关键词: Membrane proteins;    Vaccinia virus;    Crystal structure;    Membrane fusion;    Protein structure;    Recombinant proteins;    Viral structure;    Viral entry;   

DOI  :  10.1371/journal.ppat.1003563

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Vaccinia virus envelope protein A27 has multiple functions and is conserved in the Orthopoxvirus genus of the poxvirus family. A27 protein binds to cell surface heparan sulfate, provides an anchor for A26 protein packaging into mature virions, and is essential for egress of mature virus (MV) from infected cells. Here, we crystallized and determined the structure of a truncated form of A27 containing amino acids 21–84, C71/72A (tA27) at 2.2 Å resolution. tA27 protein uses the N-terminal region interface (NTR) to form an unexpected trimeric assembly as the basic unit, which contains two parallel α-helices and one unusual antiparallel α-helix; in a serpentine way, two trimers stack with each other to form a hexamer using the C-terminal region interface (CTR). Recombinant tA27 protein forms oligomers in a concentration-dependent manner in vitro in gel filtration. Analytical ultracentrifugation and multi-angle light scattering revealed that tA27 dimerized in solution and that Leu47, Leu51, and Leu54 at the NTR and Ile68, Asn75, and Leu82 at the CTR are responsible for tA27 self-assembly in vitro. Finally, we constructed recombinant vaccinia viruses expressing full length mutant A27 protein defective in either NTR, CTR, or both interactions; the results demonstrated that wild type A27 dimer/trimer formation was impaired in NTR and CTR mutant viruses, resulting in small plaques that are defective in MV egress. Furthermore, the ability of A27 protein to form disulfide-linked protein complexes with A26 protein was partially or completely interrupted by NTR and CTR mutations, resulting in mature virion progeny with increased plasma membrane fusion activity upon cell entry. Together, these results demonstrate that A27 protein trimer structure is critical for MV egress and membrane fusion modulation. Because A27 is a neutralizing target, structural information will aid the development of inhibitors to block A27 self-assembly or complex formation against vaccinia virus infection.

【 授权许可】

CC BY