Chimeric virus-like particle formation of adeno-associated virus

Adeno-associated virus (AAV) capsids are composed of three proteins, VP1, V P2, and VP3. These capsid proteins have a common amino acid sequence, being expressed from different initiation codons on the same open reading frame. Although VP1 is necessary for viral infection, it is not essential for cap sid formation. The other capsid proteins, VP2 and VP3, are sufficient for c apsid formation, but their functions are poorly understood, To investigate the role(s) of the capsid proteins in capsid formation, we used a baculovir us protein expression system to produce virus-like particles (VLPs). We fou nd that varying the ratios of VP2 and VP3 did not affect VLP formation, Fur ther, their physical properties were equivalent to those of empty wild-type particles. The function of VP3 was studied further by fusing a peptide tag , FLAG, to its N-terminus, This chimeric viral protein, in combination with VP2, could assemble into VLPs, indicating that the chimerism of VP3 did no t affect VLP formation. Although the monomeric native form of the FLAG-VP3 chimera could react with anti-FLAG antibody, VLP containing the chimeric VP 3 could not, suggesting that the N-terminal region of VP3 is located inside the VLP. These observations indicate that it may be possible to utilize AA V VLP as vectors of a broad range of drugs since fusion of the VP3 N-termin us with defined molecules could impose distinct physical properties onto th e internal environment of the VLP. (C) 1999 Academic Press.