3.7. HBV L Interacts with ERGIC-53 in a N146-Glycan-Dependent Manner
Accordingly, we next investigated whether there might be physical links between the viral N-glycan and cellular ERGIC-53. As above, HuH-7 cells were depleted for Sec24A in order to arrest ERGIC-53 within the ER, following a retransfection with the wt replicon construct or the envelope-defective HBV.Envminus replicon trans-complemented with Env.N146D. In control cells, neither the wt L nor the L.N146D mutant exhibited any colocalization with the tubulovesicular clusters stained with anti-ERGIC-53 (Figure 7). Upon depletion of Sec24A, the ERGIC-53-specific labeling pattern changed and again appeared in ER-like reticular areas. Importantly, this pattern strongly coincided with the CS structure of wt L (Figure 7A) but poorly with the CS structure of L.N146D (Figure 7B). To corroborate these findings, CO-IP analyses were performed. Since ERGIC-53/cargo interactions are known to be transient and short-lived [42,50], we here used the ectopic expression of a Myc-tagged ERGIC-53 construct together with the wt or mutant HBV replicons. As shown in Figure 7C, wt L, but not L.N146D, efficiently coprecipitated ERGIC-53. Together, these results point to a productive interaction between L and ERGIC-53 that is primary mediated by the N146-linked glycan.