Cross-species permissivity: structure of a goat adeno-associated virus and its complex with the human receptor, AAVR

Abstract

Adeno-associated virus (AAV) is a small ssDNA satellite virus of high interest (in recombinant form) as a safe and effective gene therapy vector. AAVs human cell entry receptor (AAVR) contains Polycystic Kidney Disease (PKD) domains bound by AAV. Seeking understanding of the spectrum of interactions, goat AAVGo.1 is investigated, because its host is the species most distant from human with reciprocal cross-species cell susceptibility. The structure of AAVGo.1, solved by cryo-EM to 2.9 [A] resolution, is most similar to AAV5. Through ELISA studies, it is shown that AAVGo.1 binds to human AAVR (huAAVR) more strongly than do AAV2 or AAV5, and that it joins AAV5 in a class that binds exclusively to PKD domain 1 (PKD1), in contrast to other AAVs that interact primarily with PKD2. The AAVGo.1 cryo-EM structure of a complex with a PKD12 fragment of huAAVR at 2.4 [A] resolution shows PKD1 bound with minimal change in virus structure, except for disordering of a neighboring surface loop. Only 4 of the 42 capsid protein sequence differences between AAVGo.1 and AAV5 occur at the PKD1 binding interface. These result in only minor conformational changes in AAVR, including a near rigid domain rotation with maximal displacement of the receptor by ~1 [A]. A picture emerges of two classes of AAV with completely different modes of binding to the same AAVR receptor, but within each class atomic interactions are mostly conserved. IMPORTANCEAdeno-Associated Virus (AAV) is a small ssDNA satellite parvovirus. As a recombinant vector with a protein shell encapsidating a transgene, recombinant AAV (rAAV) is a leading delivery vehicle for gene therapy with two FDA-approved treatments and 150 clinical trials for 30 diseases. The human entry receptor huAAVR has five PKD domains. To date, all serotypes, except AAV5, have interacted primarily with the second PKD domain, PKD2. Goat is the AAV host most distant from human with cross-species cell infectivity. AAVGo.1 is similar in structure to AAV5, the two forming a class with a distinct mode of receptor-binding. Within the two classes, binding interactions are mostly conserved, giving an indication of the latitude available in modulating delivery vectors.