ABSTRACT
Minor group human rhinoviruses (HRVs) bind three members of the low-density lipoprotein receptor (LDLR) family: LDLR proper, very-LDLR (VLDLR) and LDLR-related protein (LRP). Whereas ICAM-1, the receptor of major group HRVs actively contributes to viral uncoating, LDLRs are rather considered passive vehicles for cargo delivery to the low-pH environment of endosomes. Since the Tyr-Trp-Thr-Asp beta-propeller domain of LDLR has been shown to be involved in the dissociation of bound LDL via intramolecular competition at low pH, we studied whether it also plays a role in HRV infection. Human cell lines deficient in LDLR family proteins are not available. Therefore, we used CHO-ldla7 cells that lack endogenous LDLR. These were stably transfected to express either wild-type (wt) human LDLR or a mutant with a deletion of the beta-propeller. When HRV2 was attached to the propeller-negative LDLR, a lower pH was required for conversion to subviral particles than when attached to wt LDLR. This indicates that high-avidity receptor binding maintains the virus in its native conformation. HRV2 internalization directed the mutant LDLR but not wt LDLR to lysosomes, resulting in reduced plasma membrane expression of propeller-negative LDLR. Infection assays using a CHO-adapted HRV2 variant showed a delay in intracellular viral conversion and de novo viral synthesis in cells expressing the truncated LDLR. Our data indicate that the beta-propeller attenuates the virus-stabilizing effect of LDLR binding and thereby facilitates RNA release from endosomes, resulting in the enhancement of infection. This is a nice example of a virus exploiting high-avidity multimodule receptor binding with an intrinsic release mechanism.
Subject(s)
Picornaviridae Infections/metabolism , Protein Structure, Secondary , Receptors, LDL/chemistry , Receptors, LDL/metabolism , Rhinovirus/physiology , Virus Internalization , Animals , CHO Cells , Cricetinae , Cricetulus , HeLa Cells , Humans , Hydrogen-Ion Concentration , Lipoproteins, LDL/metabolism , Lysosomes/metabolism , Mutation , RNA, Viral/genetics , RNA, Viral/metabolism , Receptors, LDL/genetics , Virus AttachmentABSTRACT
X-ray structures of human rhinovirus 2 (HRV2) in complex with soluble very-low-density lipoprotein receptors encompassing modules 1, 2, and 3 (V123) and five V3 modules arranged in tandem (V33333) demonstrates multi-modular binding around the virion's five-fold axes. Occupancy was 60% for V123 and 100% for V33333 explaining the high-avidity of the interaction. Surface potentials of 3D-models of all minor group HRVs and K-type major group HRVs were compared; hydrophobic interactions between a conserved lysine in the viruses and a tryptophan in the receptor modules together with coulombic attraction via diffuse opposite surface potentials determine minor group HRV receptor specificity.
