Figure 5.

Dual GPCR and GAG inhibition by M3. (A) Surface representation of CCL2 is shown, with previously identified GAG-binding residues labeled (references 35, 44). Four out of the six residues defined by mutational analysis as creating the GAG-binding epitope of CCL2 are directly contacted by M3 and are colored blue (Arg¹⁸, Lys¹⁹, Arg²⁴, and Lys⁴⁹), whereas the noncontacted residues are colored gray (Lys⁵⁸ and His⁶⁶). The M3 NTD s2b-s3 loop is displayed in cyan, with acidic contact residues E⁸⁰ and E⁸¹ shown in stick form. (B) M3 contacts two out of the four previously identified GAG-binding residues of XCL1 (R23 and R43, blue; K25 and R70, gray; reference 38). (C) The structure of human CXCL10 (reference 70) is shown, with the four conserved GAG-binding residues identified by mutational analysis in mouse IP-10 highlighted in blue (R22, K26, K46, and K47; reference 45). (D) The structure of CCL5 is shown, with GAG-binding residues established by structural and mutational analysis highlighted in blue (R44, K45, and R47; references 46, 47). (E) Proposed model for the disruption of chemokine gradients by M3 during MHV68 infection. (F) Schematic of M3 NTD-mediated disruption of chemokine interactions with cell-surface GAGs (green) and CTD-mediated disruption of chemokine interactions with GPCRs (violet). The electrostatic potential is indicated by red (+) and blue (−) on chemokines and GAGs, respectively.