Provided are engineered viral vectors, compositions comprising viral vectors, and methods of producing and using engineered viral vectors. The engineered viral vectors provided herein include capsid proteins derived from densovirus (DNV). Such DNV capsid proteins can assemble in mammalian cells and encapsulate adeno-associated virus (AAV) and/or DNV genomic DNA. The engineered viral vectors may be used as delivery vectors in target gene therapies.

The disclosure is directed in part to variant capsid polypeptides that can be used to deliver payloads.

The present disclosure relates to the technical field of molecular biology, and in particular to an adeno-associated virus structural plasmid capable of improving adeno-associated virus titer, which is provided with a Rep gene expression cassette and a Cap gene expression cassette in sequence in the gene expression direction. The Rep gene expression cassette includes a rep gene regulated and transcribed by a first promoter, and a transcription termination signal fragment is arranged behind the rep gene; the Cap gene expression cassette includes a cap gene regulated and transcribed by a second promoter, wherein the first promoter includes any one of a P5 promoter, an RSV promoter, an MMTV promoter, a UBC promoter, and a U6 promoter, and the second promoter includes one or more of a CMV promoter, a CBh promoter, a CAG promoter, an EF1 promoter, and an SFFV promoter.