An ectromelia virus profilin homolog interacts with cellular tropomyosin and viral A-type inclusion protein
Date
2007-07-24
Authors
Butler-Cole, Christine
Wagner, Mary J
Da Silva, Melissa
Brown, Gordon D
Burke, Robert D
Upton, Chris
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: Profilins are critical to cytoskeletal dynamics in eukaryotes; however, little is known
about their viral counterparts. In this study, a poxviral profilin homolog, ectromelia virus strain
Moscow gene 141 (ECTV-PH), was investigated by a variety of experimental and bioinformatics
techniques to characterize its interactions with cellular and viral proteins.
Results: Profilin-like proteins are encoded by all orthopoxviruses sequenced to date, and share
over 90% amino acid (aa) identity. Sequence comparisons show highest similarity to mammalian
type 1 profilins; however, a conserved 3 aa deletion in mammalian type 3 and poxviral profilins
suggests that these homologs may be more closely related. Structural analysis shows that ECTVPH
can be successfully modelled onto both the profilin 1 crystal structure and profilin 3 homology
model, though few of the surface residues thought to be required for binding actin, poly(L-proline),
and PIP2 are conserved. Immunoprecipitation and mass spectrometry identified two proteins that
interact with ECTV-PH within infected cells: alpha-tropomyosin, a 38 kDa cellular actin-binding
protein, and the 84 kDa product of vaccinia virus strain Western Reserve (VACV-WR) 148, which
is the truncated VACV counterpart of the orthopoxvirus A-type inclusion (ATI) protein. Western
and far-western blots demonstrated that the interaction with alpha-tropomyosin is direct, and
immunofluorescence experiments suggest that ECTV-PH and alpha-tropomyosin may colocalize to
structures that resemble actin tails and cellular protrusions. Sequence comparisons of the poxviral
ATI proteins show that although full-length orthologs are only present in cowpox and ectromelia
viruses, an ~ 700 aa truncated ATI protein is conserved in over 90% of sequenced orthopoxviruses.
Immunofluorescence studies indicate that ECTV-PH localizes to cytoplasmic inclusion bodies
formed by both truncated and full-length versions of the viral ATI protein. Furthermore,
colocalization of ECTV-PH and truncated ATI protein to protrusions from the cell surface was
observed.
Conclusion: These results suggest a role for ECTV-PH in intracellular transport of viral proteins
or intercellular spread of the virus. Broader implications include better understanding of the virushost
relationship and mechanisms by which cells organize and control the actin cytoskeleton.
Description
BioMed Central
Keywords
Citation
Butler-Cole C. et al. An ectromelia virus profilin homolog interacts with cellular tropomyosin and viral A-type inclusion protein. Virology Journal 2007, 4 :76