Role for amino acids 212KLR214 of Ebola virus VP40 in assembly and budding

Ebola virus VP40 is able to produce virus-like particles (VLPs) in the absence of other viral proteins. At least three domains within VP40 are thought to be required for efficient VLP release: the late domain (L-domain), membrane association domain (M-domain), and self-interaction domain (I-domain). While the L-domain of Ebola VP40 has been well characterized, the exact mechanism by which VP40 mediates budding through the M- and I-domains remains unclear. To identify additional domains important for VP40 assembly/budding, amino acids (212)KLR(214) were targeted for mutagenesis based on the published crystal structure of VP40. These residues are part of a loop connecting two beta sheets in the C-terminal region and thus are potentially important for overall structure and/or oligomerization of VP40. A series of alanine substitutions were generated in the KLR region of VP40, and these mutants were examined for VLP budding, intracellular localization, and oligomerization. Our results indicated that (i) (212)KLR(214) residues of VP40 are important for efficient release of VP40 VLPs, with Leu213 being the most critical; (ii) VP40 KLR mutants displayed altered patterns of cellular localization compared to that of wild-type VP40 (VP40-WT); and (iii) self-assembly of VP40 KLR mutants into oligomers was altered compared to that of VP40-WT. These results suggest that (12)KLR(214) residues of VP40 are important for proper assembly/oligomerization of VP40 which subsequently leads to efficient budding of VLPs.