A33R Antibody

Structure and Function of the A33 Protein

The A33 protein is a type II transmembrane glycoprotein with:

• A cytoplasmic N-terminal domain

• A transmembrane region

• An extracellular C-type lectin-like domain (CTLD)

• Six cysteine residues, including C62 critical for intermolecular disulfide bonding

A33R Antibody Characteristics

Monoclonal antibodies (MAbs) against A33 exhibit:

• Conformational specificity: Most MAbs (e.g., MAb-10F10) recognize disulfide-bonded dimers, not linear epitopes .

• Neutralizing activity: Five of seven murine MAbs neutralized EEV in the presence of complement .

• Cross-species protection: Antibody A27D7 binds variola, monkeypox, and ectromelia virus A33 homologs .

Neutralizing Antibody Comparison

Mechanisms of Antibody-Mediated Protection

A33R antibodies inhibit viral spread through:

1. Neutralization: Blocking EEV binding to host cells .

2. Actin tail suppression: Disrupting A33-A36R interactions required for actin polymerization .

3. Complement activation: Enhancing phagocytosis or virolysis .

Key findings:

• Passive transfer of A33 MAbs protects mice from lethal poxvirus challenges .

• A33 C62S mutants (lacking disulfide bonds) retain immunogenicity, suggesting monomeric A33 is sufficient for vaccine design .

• Deletion of A33R abolishes antibody-resistant cell-to-cell spread, highlighting its role in evading host immunity .

Preclinical Successes

• H2 human MAb: Reduced viral titers by >90% in vitro and provided 100% survival in lethal mousepox models .

• Subunit vaccines: Recombinant A33 protein vaccines induce durable neutralizing antibodies in humans .

Challenges

• Epitope conservation: Some MAbs fail to bind variola A33 due to N125 glycosylation differences .

• Conformational dependence: Most MAbs lose efficacy if A33 is denatured .