The cowpox virus SPI-3 and myxoma virus SERP1 serpins are not functionally interchangeable despite their similar proteinase inhibition profiles in vitro.
The myxoma virus (MYX) serpin SERP1 is a secreted glycoprotein with anti-inflammatory activity that is required for full MYX virulence in vivo. The cowpox virus (CPV) serpin SPI-3 (vaccinia virus ORF K2L) is a nonsecreted glycoprotein that blocks cell-cell fusion, independent of serpin activity, and is not required for virulence of vaccinia virus or CPV in mice. Although SPI-3 has only 29% overall identity to SERP1, both serpins have arginine at the P1 position in the reactive center loop, and SPI-3 has a proteinase inhibitory profile strikingly similar to that of SERP1 [Turner, P. C., Baquero, M. T., Yuan, S., Thoennes, S. R., and Moyer, R. W. (2000) Virology 272, 267-280]. To determine whether SPI-3 and SERP1 were functionally equivalent, a CPV variant was constructed where the SPI-3 gene was deleted and replaced with the SERP1 gene regulated by the SPI-3 promoter. Cells infected with CPVDeltaSPI-3::SERP1 secrete SERP1 and show extensive fusion, suggesting that SERP1 is unable to functionally substitute for SPI-3 in fusion inhibition. In the reciprocal experiment, both copies of SERP1 were deleted from MYX and replaced with SPI-3 under the control of the SERP1 promoter. Cells infected with the MYXDeltaSERP1::SPI-3 recombinant unexpectedly secreted SPI-3, suggesting either that the cellular secretory pathway is enhanced by MYX or that CPV encodes a protein that prevents SPI-3 secretion. MYXDeltaSERP1::SPI-3 was as attenuated in rabbits as MYXDeltaSERP1::lacZ, indicating that SPI-3 cannot substitute for SERP1 in MYX pathogenesis.
Wang
Y X
YX
Department of Molecular Genetics and Microbiology, College of Medicine, Gainesville, Florida, 32610, USA.
Turner
P C
PC
Ness
T L
TL
Moon
K B
KB
Schoeb
T R
TR
Moyer
R W
RW
D000818:Animals; D002459:Cell Fusion; D002460:Cell Line; D015608:Cowpox virus / Q000201:enzymology* / Q000502:physiology*; D006031:Glycosylation; D008297:Male; D051379:Mice; D009233:Myxoma virus / Q000201:enzymology* / Q000502:physiology*; D009234:Myxomatosis, Infectious / Q000201:enzymology / Q000821:virology; D016366:Open Reading Frames / Q000235:genetics; D010641:Phenotype; D011817:Rabbits; D011995:Recombination, Genetic; D015842:Serine Proteinase Inhibitors / Q000378:metabolism*; D015843:Serpins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014616:Vaccinia virus / Q000201:enzymology / Q000502:physiology; D014760:Viral Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D014764:Viral Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
D015842:Serine Proteinase Inhibitors; D015843:Serpins; D014760:Viral Fusion Proteins; D014764:Viral Proteins