A zinc ion controls assembly and stability of the major capsid protein of rotavirus

Area of Science:

• Structural Biology
• Virology
• Protein Biochemistry

Background:

• The crystal structure of rotavirus VP6, the major capsid protein, reveals a trimer with a central zinc ion coordinated by histidine residues.
• The function of this zinc ion in VP6 assembly and stability remains largely uncharacterized.

Purpose of the Study:

• To investigate the role of the zinc ion coordinated by histidine 153 in the function and assembly of rotavirus VP6.
• To determine if zinc is essential for VP6 trimer formation, assembly into characteristic structures, and transcriptase activity.

Main Methods:

• Site-directed mutagenesis was used to alter histidine 153 residues in VP6.
• Wild-type and mutant VP6 proteins were analyzed for trimer formation, assembly properties at different pH values, and susceptibility to proteases.
• Zinc depletion using a metal-chelating agent and assembly on cores with transcriptase activity rescue assays were performed.

Main Results:

• Mutations at histidine 153 did not prevent VP6 trimer formation but affected assembly into tubes at pH > 7.0.
• Zinc-depleted wild-type VP6 exhibited similar assembly defects as the histidine mutants.
• Absence of zinc increased VP6 susceptibility to proteases, particularly affecting the alpha-helical basal domain.
• Mutant VP6 proteins assembled on cores and rescued transcriptase activity, indicating zinc is not required for transcription.

Conclusions:

• The zinc ion coordinated by histidine 153 plays a critical role in controlling the structural flexibility and assembly of VP6 trimers, particularly at neutral to alkaline pH.
• Zinc is essential for the proper formation of rotavirus-like tubes but not for VP6 trimerization or viral transcriptase activity.
• These findings elucidate the structural contribution of zinc to rotavirus capsid protein function and stability.