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Mapping the sialic acid-binding sites of LuIII and H-1 parvovirus
Kevin Busuttil1, Nikéa Pittman1, Jon Zachary1
1Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida, USA.
Abstract:
Oncolytic protoparvoviruses, including LuIII, H-1 parvovirus (H-1PV), and the prototypic strain of minute virus of mice (MVMp), can target and destroy cancer cells. Host cell targeting is based largely on the identification and interaction of the virus with the primary receptor. Previously, it has been shown that MVMp and H-1PV bind to sialic acid (SIA), which is the primary glycan receptor. This study investigates whether LuIII also utilizes a similar glycan for host cell attachment. Microarray analysis confirmed that α2-3-linked SIA is a shared receptor requirement for cell binding for all three viruses. Three glycans were identified in the array, namely, Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4GlcNAc, Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4GlcNAcβ1-3Galβ1-4GlcNAc, and Neu5Acα2-3Galβ1-4(Fucα1-3)-GlcNAcβ1-3-Galβ1-4(Fucα1-3)-GlcNAc. The cryo-EM structures of the LuIII and H-1PV glycan complexes were determined to resolutions ranging from 2.57 to 2.88 Å. Small structural perturbations were observed between the cryo-EM map and the previous X-ray crystallographic maps for H-1PV, including several histidine residues within the HI loop. Overall, LuIII and H-1PV utilize a shared SIA recognition pocket near the icosahedral twofold axis adjacent to (but not overlapping with) the known MVMp SIA binding site. In addition, structural differences between the major capsid protein (VP2) of LuIII, H-1PV, and MVMp all clustered around these glycan-binding pockets. This structural phenotype may contribute to the differences observed in tumor cell killing efficiency among the rodent protoparvoviruses.
Importance:
Oncolytic viruses could provide a safe alternative for targeting aggressive tumors that evade standard therapies. While rodent protoparvoviruses are innocuous in non-cancerous cells, they carry out efficient cell killing in tumors. Differences in cell tropism and killing efficiency are determined by the viral capsid proteins; thus, structural studies provide insight into understanding the protoparvovirus infection in both wild-type and cancerous cells. Binding to extracellular sialic acid (SIA) initiates cell entry for protoparvoviruses H-1PV, MVMp, and this is also hypothesized for LuIII. This study investigates the structures of LuIII and H-1PV in the presence of their glycan receptors to identify and map the capsid loci that are responsible for this interaction. This knowledge may aid future capsid engineering to improve oncolytic targeting efficiency.
Insights
Oncolytic protoparvoviruses like LuIII and H-1PV bind to sialic acid (SIA) for cell entry. Structural analysis reveals shared SIA binding pockets, explaining differences in tumor cell killing efficiency.
Area of Science:
- Virology
- Structural Biology
- Oncology
Background:
- Oncolytic viruses offer a promising strategy for targeting aggressive tumors resistant to conventional treatments.
- Rodent protoparvoviruses, such as H-1PV, MVMp, and LuIII, exhibit selective oncolytic activity, targeting cancer cells while sparing healthy ones.
- Viral capsid-glycan interactions, particularly with sialic acid (SIA), are crucial for determining viral tropism and oncolytic efficacy.
Purpose of the Study:
- To investigate the glycan receptor usage of LuIII and elucidate the structural basis of its interaction with sialic acid (SIA).
- To determine the cryo-electron microscopy (cryo-EM) structures of LuIII and H-1PV in complex with their glycan receptors.
- To compare the glycan-binding sites of LuIII and H-1PV with MVMp to understand variations in oncolytic activity.
Main Methods:
- Microarray analysis to identify glycan receptor requirements for LuIII, H-1PV, and MVMp binding.
- Cryo-electron microscopy (cryo-EM) to determine the high-resolution structures of LuIII-glycan and H-1PV-glycan complexes.
- Comparative structural analysis of viral capsid proteins (VP2) to map glycan-binding pockets.
Main Results:
- Microarray analysis confirmed that α2-3-linked sialic acid (SIA) is a shared receptor for LuIII, H-1PV, and MVMp.
- Cryo-EM structures revealed that LuIII and H-1PV share a similar SIA recognition pocket near the icosahedral twofold axis, distinct from the MVMp binding site.
- Structural differences in the VP2 capsid protein around the glycan-binding pockets were observed among the three viruses.
Conclusions:
- LuIII, H-1PV, and MVMp utilize sialic acid as a common glycan receptor for host cell attachment.
- Shared and distinct structural features of SIA binding pockets in LuIII and H-1PV, compared to MVMp, contribute to their specific cell tropism.
- Understanding these structural variations in glycan-binding sites is essential for potentially engineering improved oncolytic parvoviruses for cancer therapy.
