How does the bean-pod mottle virus (BPMV) capsid structure differ from that of HRV?

Sourav PanOctober 28, 2024

Answered

The capsid structures of the bean-pod mottle virus (BPMV) and human rhinovirus (HRV) exhibit several key differences, reflecting their distinct viral architectures and structural characteristics. Here are the main differences:

1. Subunit Composition:
   • BPMV: The BPMV capsid is composed of only two types of subunits: a small subunit and a large subunit. The small subunit contains one β-barrel domain, while the large subunit contains two β-barrel domains that remain covalently attached.
   • HRV: In contrast, HRV capsids are made up of three different types of subunits: VP1, VP2, and VP3. Each of these subunits has a distinct structure and contributes to the overall architecture of the capsid.
2. Capsid Size:
   • BPMV: The BPMV capsid has a diameter of approximately 320 Å, which is similar to that of HRV but is constructed differently due to its fewer subunit types.
   • HRV: HRV also has a diameter of about 320 Å, but its structure is more complex due to the presence of three different capsid proteins.
3. Assembly and Quasi-Symmetry:
   • BPMV: The BPMV capsid assembles into a T = 3-like shell, where the small subunit is equivalent to VP1 in HRV, and the large subunit corresponds to VP2 and VP3. This assembly is characterized by a simpler arrangement of fewer subunit types.
   • HRV: HRV exhibits a T = 3 quasi-symmetry, where the three different subunits (VP1, VP2, and VP3) are arranged in a more complex manner, contributing to the formation of a viral canyon that is important for receptor binding.
4. Structural Features:
   • BPMV: The BPMV capsid structure features a more straightforward assembly with its two subunits, which can lead to a more uniform surface topology.
   • HRV: The HRV capsid has a distinct “viral canyon” that encircles the fivefold axes, which is a deep cleft that plays a critical role in binding to cellular receptors (such as ICAM-1). This feature is not present in BPMV.
5. Protein Folding and Interactions:
   • BPMV: The folding of the BPMV subunits into β-barrel domains allows for effective assembly, but the interactions are less complex due to the reduced number of subunit types.
   • HRV: The VP1, VP2, and VP3 subunits in HRV exhibit more complex folding patterns and interactions, which contribute to the structural diversity and functional capabilities of the capsid.
6. Functionality and Host Interaction:
   • BPMV: The simpler structure of BPMV may influence its interactions with host cells and its overall functionality, particularly in plant hosts.
   • HRV: The more complex structure of HRV, including the viral canyon, is specifically adapted for interactions with human cell receptors, facilitating its entry into host cells.