L4 - Viral structure Flashcards
What is icosahedral symmetry and why is it common in viruses?
Icosahedral symmetry refers to a spherical arrangement with 20 triangular faces and 12 vertices. It optimises structural stability, allows efficient assembly with minimal genetic material, and features 2-, 3-, and 5-fold rotational symmetry axes.
What characterises helical virus structures, and how do they differ from icosahedral structures?
Helical viruses have a spiral or rod-like nucleocapsid, often seen in enveloped RNA viruses. Unlike icosahedral viruses, which form spherical capsids, helical viruses can flexibly encapsidate long RNA strands.
Why is understanding virus symmetry important for structural studies?
It aids in determining the assembly, stability, and potential targets for antiviral drugs.
Why is cryo-electron microscopy (cryo-EM) a powerful tool for studying virus structure?
Cryo-EM preserves viruses in their native hydrated state via rapid freezing, avoiding crystal formation. It enables high-resolution 3D reconstructions, especially useful for large or dynamic viruses.
How does X‑ray crystallography contribute to our understanding of virus structure?
It provides atomic resolution details of virus components, although it requires the virus or its parts to form crystals.
What role does cryo-electron tomography play in virus research?
It allows for visualisation of large, asymmetrical biological assemblies, including viruses in a near-native state.
How have AI approaches, such as AlphaFold, advanced virus structural studies?
They refine cryo-EM reconstructions, predict protein structures from sequences, and aid in mapping evolutionary relationships.
What was significant about the X‑ray structure determination of poliovirus?
It showed the “β-jelly roll” structure of capsid proteins, a fundamental motif informing our understanding of virus assembly and stability.
What is the benefit of combining X‑ray and cryo‑EM techniques in viral studies?
This integration enables a comprehensive view of viral structure—high-resolution atomic details from X-ray with broader, dynamic context from cryo-EM.
How does knowledge of virus structure support drug and vaccine development?
Structural insights identify viral protein domains and binding sites, allowing for the rational design of vaccines, antiviral drugs, and strategies to attenuate viruses.
What are the key areas covered in the study of virus structure?
The study includes virus symmetry, methods to determine structures (e.g. cryo-EM, X‑ray crystallography), atomic-resolution structures, and applications such as antiviral drug design and vaccine development.
How has structural knowledge advanced our understanding of virus entry and evolution?
Detailed structures reveal dynamic rearrangements during entry, inform fusion mechanisms, and help trace evolutionary relationships among viruses.
Why is it important to study virus structure at atomic resolution?
Atomic-level details allow for precise identification of functional domains, interactions with host receptors, and targeted design of antiviral compounds.
In what ways is virus structure utilised in modern medicine?
It is applied to structure-based vaccine design, rational drug design, and even the attenuation of viruses for safe vaccine development.
Why is icosahedral symmetry advantageous for virus assembly?
It allows viruses to form a closed shell using multiple copies of a few protein types, minimising genetic complexity while maximising structural strength.
In what types of viruses are helical structures typically observed?
They are common in many enveloped animal RNA viruses, such as those in the Paramyxoviridae family.
What are the main techniques used to study virus structure?
Key methods include electron microscopy (EM), cryo-electron microscopy (cryo-EM), and X‑ray crystallography.
How has the resolution of cryo-EM advanced in recent years?
Cryo-EM resolution has improved to below 2 Å, allowing for near-atomic detail in virus structures.
How has the structure of influenza haemagglutinin (HA) contributed to our knowledge of virus entry?
The X‑ray structure of HA delineated receptor-binding and fusion domains, clarifying how the virus binds to host cells and initiates fusion
Why are structural studies of viruses critical for developing antiviral therapies?
Detailed structures enable the design of molecules that specifically target viral components, disrupting key processes such as fusion and replication.
How are X‑ray and cryo‑EM techniques combined to study flaviviruses?
X‑ray crystallography provides atomic details of individual proteins, while cryo‑EM visualises the intact virus particle and its overall architecture.
What is the advantage of combining these two methods for flaviviruses?
The integration allows researchers to map high-resolution protein structures onto the overall virion, revealing how structural rearrangements occur during maturation and fusion.
How does the flavivirus E protein change upon exposure to acidic pH?
It undergoes a conformational rearrangement from a dimeric to a trimeric postfusion state, facilitating membrane fusion.
What are some applications of the structural knowledge obtained from flavivirus studies?
These include rational vaccine design, antiviral drug development, and improved understanding of virus-host interactions and immune evasion.
