The hydrophobic nature of dengue 2 M residue 36 influences E protein and ApoptoM peptide

The recent epidemics of dengue in South West Indian Ocean coincided with the emergence of Cosmopolitan dengue virus type 2, including viral strains DES-14 in Tanzania and then RUN-18 in La Reunion. The initial step of dengue virus assembly is the formation of heterodimers between prM and E proteins where prM acts as a chaperone for E. During dengue virus maturation, prM is cleaved into membrane protein M which embeds a pro-apoptotic peptide consisting of residues 31/41 and referred as ApoptoM. An infrequent valine at position M-36 was found in DES-14 whereas RUN-18 bears a common isoleucine. Here, we investigated whether Ile-to-Val substitution at position M-36 may have an impact on RUN-18 E expression and cell-death promoting capability of RUN-18 ApoptoM. Using recombinant RUN-18 envelope proteins expressed in human epithelial A549 cells, we showed that Ile-to-Val but not Ile-to-Ala substitution affects the behavior E protein reducing the cytotoxicity of prM and E proteins. The substitution of isoleucine by valine at position M-36 leads to increase the apoptosis-inducing activity of ApoptoM. Our data highlight that hydrophobic nature of amino-acid residue in position 36 of dengue virus M protein influences E protein expression and death-promoting activity of ApoptoM opens up important perspectives in the development of effective live-attenuated DENV vaccines.