3-D Model of AAV Capsid Structure (IMAGE) University of Pennsylvania School of Medicine Caption A 3-D model of adeno-associated virus (AAV) capsid structure: AAV capsid sixty subunits assemble to generate the icosahedral symmetric virus capsid. The viral asymmetric unit of the capsid is bounded by 5-fold, 3-fold, and 2-fold symmetry axes. The capsid external surface features are formed by the subunit hyper-variable loops. Credit Katherine Hinkel, University of Pennsylvania Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.