On assays were carried out using ephrinB2, ephrin-B3 or G-specific polyclonal antibodies as a control (Figure 7). Each HeV-G glycoprotein mutant was also precipitated from an equivalent amount of lysate with polyclonal antibodies as a control. The results from these experiments were somewhat unexpected as very few of the targeted residues had any measurable effect on the HeV-G/purchase 194423-15-9 ephrin-B2 association by coimmunoprecipitation, with only W504A showing a significant disruption of ephrin-B2 binding in comparison to wild-type HeVG (Figure 7A). By comparison however, the majority of the HeVG mutants (Q490A, E501A, W504A, E505A, G506A, and Y581A) revealed a significant disruption in their ability to bind to ephrinB3 (Figure 7A). No differences were observed in the ephrin-B2 or ephrin-B3 binding profiles by any of the HeV-G mutants or wildtype HeV-G when the HeV-F glycoprotein was co-expressed (Figure 7B).Figure 5. 101043-37-2 Rearrangement of the receptor binding face of HeV-G upon ephrin-B2 binding. Complexed HeV-G (yellow) is superimposed with unbound HeV-Gs (green and cyan, which represent two different molecules within the same asymmetric unit). The interface between the two HeV-G molecules within the unbound HeV-G homodimer is colored in red. The G-H loop of ephrin-B2 is colored in purple. The ephrin-B2-contacting regions of HeV-G are colored in pink. Receptor binding causes a dramatic conformational change in the B6S2-B6S3 loop region, which then disrupts the HeV-G homodimerization interface observed in the unbound HeV-G. doi:10.1371/journal.pone.0048742.gchain to the “up” rotamer conformation results in a snug fit into the binding groove with its amine group facing the electrostatically negative environment of E505, Q490. This conformation is further stabilized by van der Waals interactions with residue L124 of ephrin-B2. We postulate that the “up” rotamer is an intermediate state and the W122 side chain rotates into the final “down” rotamer conformation, reducing its energy by creating an intricate van der Waals interaction network with the pocket-forming hydrophobic residues in HeV-G. This also helps secure the other three Gbinding ephrin hydrophobic residues (F117, P119 and L121) firmly into their pockets, stabilizing the whole central hydrophobic region of the ephrin-G interface. Thus, the structural data supports a “lock, key and latch” model for the association between the G glycoprotein and its receptors with the W122 residue of ephrin-B2 serving as the “latch” (Figure 6C). The ephrin “latch” is transiently lifted up as shown on the left panel to facilitate the insertion of the three key hydrophobic residues (F117, P119 and L121) during association of the virus-receptor complex. When the “latch” is pulled down, as shown in the right panel, the aromatic ring edge 1527786 of W122 is propped against the wall of its binding pocket. This prevents the G-H loop from sliding out and creates an energy barrier for the withdrawal of 11967625 the other three hydrophobic ephrin residues. We propose that like most proteinprotein interactions, the henipavirus receptor attachment event is a dynamic process, during which the ephrin G-H loop inserts and withdraws from the hydrophobic cavity of G. During this process, W122 alternates between rotamers. The occupancies of the “latch-Single substitutions of HeV-G residues within the ephrinbinding interface significantly impact viral entryTo explore the correlation between HeV-G/ephrin-B2/B3 binding results with the f.On assays were carried out using ephrinB2, ephrin-B3 or G-specific polyclonal antibodies as a control (Figure 7). Each HeV-G glycoprotein mutant was also precipitated from an equivalent amount of lysate with polyclonal antibodies as a control. The results from these experiments were somewhat unexpected as very few of the targeted residues had any measurable effect on the HeV-G/ephrin-B2 association by coimmunoprecipitation, with only W504A showing a significant disruption of ephrin-B2 binding in comparison to wild-type HeVG (Figure 7A). By comparison however, the majority of the HeVG mutants (Q490A, E501A, W504A, E505A, G506A, and Y581A) revealed a significant disruption in their ability to bind to ephrinB3 (Figure 7A). No differences were observed in the ephrin-B2 or ephrin-B3 binding profiles by any of the HeV-G mutants or wildtype HeV-G when the HeV-F glycoprotein was co-expressed (Figure 7B).Figure 5. Rearrangement of the receptor binding face of HeV-G upon ephrin-B2 binding. Complexed HeV-G (yellow) is superimposed with unbound HeV-Gs (green and cyan, which represent two different molecules within the same asymmetric unit). The interface between the two HeV-G molecules within the unbound HeV-G homodimer is colored in red. The G-H loop of ephrin-B2 is colored in purple. The ephrin-B2-contacting regions of HeV-G are colored in pink. Receptor binding causes a dramatic conformational change in the B6S2-B6S3 loop region, which then disrupts the HeV-G homodimerization interface observed in the unbound HeV-G. doi:10.1371/journal.pone.0048742.gchain to the “up” rotamer conformation results in a snug fit into the binding groove with its amine group facing the electrostatically negative environment of E505, Q490. This conformation is further stabilized by van der Waals interactions with residue L124 of ephrin-B2. We postulate that the “up” rotamer is an intermediate state and the W122 side chain rotates into the final “down” rotamer conformation, reducing its energy by creating an intricate van der Waals interaction network with the pocket-forming hydrophobic residues in HeV-G. This also helps secure the other three Gbinding ephrin hydrophobic residues (F117, P119 and L121) firmly into their pockets, stabilizing the whole central hydrophobic region of the ephrin-G interface. Thus, the structural data supports a “lock, key and latch” model for the association between the G glycoprotein and its receptors with the W122 residue of ephrin-B2 serving as the “latch” (Figure 6C). The ephrin “latch” is transiently lifted up as shown on the left panel to facilitate the insertion of the three key hydrophobic residues (F117, P119 and L121) during association of the virus-receptor complex. When the “latch” is pulled down, as shown in the right panel, the aromatic ring edge 1527786 of W122 is propped against the wall of its binding pocket. This prevents the G-H loop from sliding out and creates an energy barrier for the withdrawal of 11967625 the other three hydrophobic ephrin residues. We propose that like most proteinprotein interactions, the henipavirus receptor attachment event is a dynamic process, during which the ephrin G-H loop inserts and withdraws from the hydrophobic cavity of G. During this process, W122 alternates between rotamers. The occupancies of the “latch-Single substitutions of HeV-G residues within the ephrinbinding interface significantly impact viral entryTo explore the correlation between HeV-G/ephrin-B2/B3 binding results with the f.
