title: Molluscum contagiosum virus interleukin-18 (IL-18) binding protein is secreted as a full-length form that binds cell surface glycosaminoglycans through the C-terminal tail and a furin-cleaved form with only the IL-18 binding domain.
abstract: Some poxviruses and their mammalian hosts encode homologous proteins that bind interleukin-18 (IL-18) with high affinity and inhibit IL-18-mediated immune responses. MC54L, the IL-18 binding protein of the human poxvirus that causes molluscum contagiosum, is unique in having a C-terminal tail of nearly 100 amino acids that is dispensable for IL-18 binding. When recombinant MC54L was expressed and purified via a C-terminal six-histidine tag, a shorter fragment was detected in addition to the full-length protein. This C-terminal fragment resulted from the cleavage of MC54L by cellular furin, as it was greatly diminished when furin was specifically inhibited or when a furin-deficient cell line was used for expression. Furthermore, the N- and C-terminal fragments of MC54L were generated by cleavage of the recombinant protein with furin in vitro. The furin cleavage site was mapped within a 32-amino-acid segment that is C terminal to the IL-18 binding domain. Full-length MC54L, but not the N-terminal IL-18 binding fragment, bound to cells and to purified heparin and other glycosaminoglycans that are commonly found on the cell surface and in the extracellular matrix. MC54L bound to heparin with a nanomolar K(d) and could simultaneously bind to IL-18. Their different glycosaminoglycan and cell binding properties may allow the long and short forms of MC54L to inactivate IL-18 near the site of infection and at more distal locations, respectively.
authors.affiliation: Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases/National Institutes of Health, 4 Center Drive, Bethesda, MD 20892-0445, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Xiang
authors.forename: Bernard
authors.initials: B
authors.lastname: Moss
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D045683:Furin; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006025:Glycosaminoglycans / Q000378:metabolism*; D006493:Heparin / Q000378:metabolism; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D020382:Interleukin-18 / Q000378:metabolism*; D008969:Molecular Sequence Data; D008977:Molluscum contagiosum virus / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013381:Subtilisins / Q000235:genetics / Q000378:metabolism*; D020349:Surface Plasmon Resonance
chemical_list: D006023:Glycoproteins; D006025:Glycosaminoglycans; D036341:Intercellular Signaling Peptides and Proteins; D020382:Interleukin-18; D011994:Recombinant Proteins; C118370:interleukin-18 binding protein; D006493:Heparin; D013381:Subtilisins; D045683:Furin