Two glycosaminoglycan-binding domains of the mouse cytomegalovirus-encoded chemokine MCK-2 are critical for oligomerization of the full-length protein [Immunology]

Chemokines are essential for antimicrobial host defenses and tissue repair. Herpesviruses and poxviruses also encode chemokines, copied from their hosts and repurposed for multiple functions, including immune evasion. The CC chemokine MCK-2 encoded by mouse cytomegalovirus (MCMV) has an atypical structure consisting of a classic chemokine domain N-terminal to a second unique domain, resulting from the splicing of MCMV ORFs m131 and m129. MCK-2 is essential for full MCMV infectivity in macrophages and for persistent infection in the salivary gland. However, information about its mechanism of action and specific biochemical roles for the two domains has been lacking. Here, using genetic, chemical and enzymatic analyses of multiple mouse cell lines as well as primary mouse fibroblasts from salivary gland and lung, we demonstrate that MCK-2 binds glycosaminoglycans (GAGs) with affinities in the following order: heparin > heparan sulfate > chondroitin sulfate=dermatan sulfate. Both MCK-2 domains bound these GAGs independently, and computational analysis together with site-directed mutagenesis identified five basic residues distributed across the N-terminus and the 30s and 50s loops of the chemokine domain that are important GAG-binding determinants. Both domains were required for GAG-dependent oligomerization of full-length MCK-2. Thus, MCK-2 is an atypical viral chemokine consisting of a CC chemokine domain and a unique non-chemokine domain, both of which bind GAGs and are critical for GAG-dependent oligomerization of the full-length protein.

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