Structural studies of recombinant Norwalk capsids.

Area of Science:

• Virology
• Structural Biology
• Biochemistry

Background:

• Norwalk virus is a primary cause of epidemic viral gastroenteritis in humans.
• Culturing Norwalk virus in laboratory cell lines has proven challenging.
• Recombinant baculovirus technology enables expression of Norwalk virus capsid protein in insect cells.

Purpose of the Study:

• To determine the high-resolution structure of Norwalk virus-like particles.
• To elucidate the assembly and structural characteristics of the Norwalk virus capsid.
• To investigate the structural domains of the Norwalk virus capsid protein.

Main Methods:

• Expression of Norwalk virus capsid protein in insect cells using recombinant baculovirus.
• Spontaneous assembly of virus-like particles (VLPs) from expressed capsid protein.
• X-ray crystallography to determine the 3.4 Å structure of recombinant Norwalk particles.
• Utilizing a 22 Å electron cryomicroscopy structure as a phasing model for X-ray crystallography.

Main Results:

• Recombinant Norwalk particles spontaneously assembled and exhibited T=3 icosahedral symmetry.
• The capsid structure revealed 90 arch-like capsomere dimers forming the 380 Å diameter capsid.
• The capsid protein possesses distinct shell (S) and protruding (P) domains, with the P domain exhibiting a novel viral protein structure and containing a variable surface-exposed subdomain.

Conclusions:

• The study successfully determined the high-resolution structure of Norwalk virus-like particles.
• The structural analysis provides insights into the assembly mechanism and architecture of the Norwalk virus capsid.
• The unique structure of the protruding domain suggests potential roles in viral interaction and pathogenesis.