Lack of involvement of strand s1'A of the viral serpin CrmA in anti-apoptotic or caspase-inhibitory functions.
CrmA is a cowpox virus serpin required for full host infectivity and virulence. Residues 51-56 (DKNKDD), the only region that differs significantly from related viral serpins, were investigated for functional importance. A 1.6A X-ray structure reported here showed that this region can adopt either structured or unstructured conformations. Three variants were expressed, one with the region 51-56 deleted, one substituted by alanines, and one in which this region was replaced by the sequence encoded in smallpox virus. NMR showed that the region is an exposed, flexible loop that can be deleted without perturbing the serpin. The region is also very susceptible to proteolysis. Significantly, inhibition of caspases 1 and 8 was unaffected by the mutations, and each of the variants was as effective as wild-type CrmA in promoting survival from apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Thus, although the 51-56 region of CrmA is unique, and is exposed and highly susceptible to proteolysis, any in vivo role must involve a function other than proteinase inhibition or cell sparing.
Simonovic
Miljan
M
Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, USA.
Denault
Jean-Bernard
JB
Salvesen
Guy S
GS
Volz
Karl
K
Gettins
Peter G W
PG
D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D001665:Binding Sites; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D015843:Serpins / Q000737:chemistry / Q000494:pharmacology*; D014616:Vaccinia virus / Q000737:chemistry*; D014764:Viral Proteins / Q000737:chemistry / Q000494:pharmacology*
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D008024:Ligands; D015843:Serpins; D014764:Viral Proteins; C074641:interleukin-1beta-converting enzyme inhibitor; D020169:Caspases