Title :
Complex N-linked glycans on
Asn-89 of Kaposi sarcoma herpes virus-encoded
interleukin-6 mediate optimal function by affecting cytokine
protein conformation
Abstract :
- Kaposi sarcoma-associated herpesvirus-encoded interleukin-6 ( vIL-6) and its human cellular homologue (hu IL-6 ) share similar biological functions
- Our previous work showed that N-linked glycosylation was required for optimal function of vIL6 but not hu IL-6 (1)
- Here we describe heterogeneity in the com position of the glycans of the two N-linked sites of vIL-6
- The Asn-89 site of vIL-6, found to be required for optimal cytokine function, is composed of complex glycans
- The Asn-78 site is composed of high mannose glycans, which are dispensable for cytokine function
- N-Linked glycosylation at the Asn-89 site was required for intracellular production of functional vIL-6, but endoglycosidase-mediated removal of N-linked glycans from secreted vIL-6 did not impair protein function
- With the use of a conformation-specific antibody and tryptic digestion assays, we showed that glycosylation at the Asn-89 site of vIL-6 affected protein conformation
- Human IL-6 , but not vIL-6, requires IL-6Ralpha for binding to gp130
- We tested the hypothesis that the Asn-89 complex glycan of vIL-6 alone was sufficient to confer binding to gp130 independently of IL-6Ralpha
- Two mutants of hu IL-6 , made to contain additional complex N-linked glycans in the region that interacts with IL-6Ralpha , did not confer binding to gp130 independently of IL-6Ralpha
- Our findings support the conclusion that complex glycans on Asn-89 of vIL-6 specifically promote a protein conformation that allows the viral cytokine to bind gp130 independently of IL-6Ralpha