Identification of complement regulatory domains in vaccinia virus complement control protein

Area of Science:

• Immunology
• Virology
• Structural Biology

Background:

• Vaccinia virus complement control protein (VCP) is a viral homolog of human complement regulators.
• VCP comprises four contiguous complement control protein (CCP) domains.
• VCP binds C3b and C4b, inactivating classical and alternative complement pathways.

Purpose of the Study:

• To map the specific CCP domains of VCP responsible for its functional activities.
• To determine which CCP domains are crucial for cofactor, decay-accelerating, and binding activities.
• To understand the structural basis for VCP's conserved four-domain structure in poxviruses.

Main Methods:

• Utilized a series of deletion mutants of VCP.
• Assessed cofactor activity for C3b and C4b inactivation.
• Measured decay-accelerating activity on classical and alternative pathway C3 convertases.
• Quantified binding affinity to target proteins C3b and C4b.

Main Results:

• CCPs 1-3 are essential for cofactor activity; CCP 4 contributes to optimal function.
• CCPs 1-2 mediate minimal classical pathway decay acceleration, requiring all four for efficiency.
• CCPs 2-4 mediate alternative pathway decay acceleration.
• CCPs 1-3 are required for C3b/C4b binding; CCP 4 enhances affinity.

Conclusions:

• The entire VCP protein, comprising all four CCP domains, is necessary for its diverse functional activities.
• The data support the conservation of the four-domain structure in viral CCPs across poxviruses.
• Understanding VCP's domain functions provides insights into viral immune evasion strategies.