Identification of the human rhinovirus serotype 1A binding site on the murine low-density lipoprotein receptor by using human-mouse receptor chimeras

Human rhinovirus serotype 1A (HRV1A) binds more strongly to the mouse low-density lipoprotein receptor (LDLR) than to the human homologue (M. Reithmayer, A. Reischl, L. Snyers, and D. Blaas, J. Virol. 76:6957-6965, 2002). Here, we used this fact to determine the binding site of HRV1A by replacing selected ligand binding modules of the human receptor with the corresponding ligand binding modules of the mouse receptor. The chimeric proteins were expressed in mouse fibroblasts deficient in endogenous LDLR and LDLR-related protein, both used by minor group HRVs for cell entry. Binding was assessed by virus overlay blots, by immunofluorescence microscopy, and by measuring cell attachment of radiolabeled virus. Replacement of ligand binding repeat 5 of the human LDLR with the corresponding mouse sequence resulted in a substantial increase in HRV1A binding, whereas substitution of repeats 3 and 4 was without effect. Replacement of human receptor repeats 1 and 2 with the murine homologues also increased virus binding. Finally, murine receptor modules 1, 2, and 5 simultaneously introduced into the human receptor resulted in HRV1A binding indistinguishable from mouse wild-type receptor. Thus, repeats 1 and/or 2 and repeat 5 are involved in HRV1A attachment. Changing CDG (GP) under barD in the acidic cluster of module 5 in the human receptor to CDG (EA) under barD present in the mouse receptor led to substantially increased binding of HRV1A, indicating an important role of the glutamate residue in HRV1A recognition.