Background:The human IgG1 antibody subclass is the most abundant one and is widely used in therapeutic applications. Results: Ultracentrifugation and x-ray/neutron scattering, together with atomistic modeling, revealed asymmetric concentration-independent IgG1 solution structures. Conclusion:The complement and receptor Fc binding sites are not hindered by the Fab regions, explaining its full activity. Significance: These solution structures clarify IgG1 activity and its therapeutic applications.

Background: The human IgG4 antibody subclass does not activate complement and forms half-antibodies.Results: Ultracentrifugation and x-ray/neutron scattering together with atomistic modeling revealed asymmetric concentration-dependent IgG4 solution structures.Conclusion: The complement and receptor Fc binding sites are hindered by the Fab regions, explaining loss of activity.Significance: These solution structures clarify IgG4 function and its therapeutic applications.

Detailed analytical ultracentrifugation and X-ray/neutron scattering data and a new atomistic modelling approach revealed asymmetric extended solution structures for human IgA1 that account for its receptor-binding function. IgA1 with different hinge O-galactosylation patterns showed similar structures.