Dimerization regulates both deaminase-dependent and deaminase-independent HIV-1 restriction by APOBEC3G

Michael Morse,Ran Huo,Mark C Williams,Ioulia Rouzina,Linda Chelico,Yuqing Feng

doi:10.1038/s41467-017-00501-y

Michael Morse, Ran Huo + Show 4 more

Open Access

https://doi.org/10.1038/s41467-017-00501-y

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Abstract

APOBEC3G (A3G) is a human enzyme that inhibits human immunodeficiency virus type 1 (HIV-1) infectivity, in the absence of the viral infectivity factor Vif, through deoxycytidine deamination and a deamination-independent mechanism. A3G converts from a fast to a slow binding state through oligomerization, which suggests that large A3G oligomers could block HIV-1 reverse transcriptase-mediated DNA synthesis, thereby inhibiting HIV-1 replication. However, it is unclear how the small number of A3G molecules found in the virus could form large oligomers. Here we measure the single-stranded DNA binding and oligomerization kinetics of wild-type and oligomerization-deficient A3G, and find that A3G first transiently binds DNA as a monomer. Subsequently, A3G forms N-terminal domain-mediated dimers, whose dissociation from DNA is reduced and their deaminase activity inhibited. Overall, our results suggest that the A3G molecules packaged in the virion first deaminate viral DNA as monomers before dimerizing to form multiple enzymatically deficient roadblocks that may inhibit reverse transcription.

Highlights

APOBEC3G (A3G) is a human enzyme that inhibits human immunodeficiency virus type 1 (HIV-1) infectivity, in the absence of the viral infectivity factor Vif, through deoxycytidine deamination and a deamination-independent mechanism
These results are consistent with the N-terminal domain (NTD) being the primary dimerization interface and with the C-terminal domain (CTD) acting as a secondary interface that allows for the formation of tetramers and larger oligomers
When bound to single-stranded DNA (ssDNA), we observe that the NTD mutant A3G (FW) remains primarily in a monomeric state, the CTD mutants (IY and RDDQ) form dimers mediated by the NTDs but are deficient in forming larger

Summary

Introduction

APOBEC3G (A3G) is a human enzyme that inhibits human immunodeficiency virus type 1 (HIV-1) infectivity, in the absence of the viral infectivity factor Vif, through deoxycytidine deamination and a deamination-independent mechanism. The subsequent use of these deoxyuridines as a template for ( + )DNA synthesis results in C-G to T-A mutations in the proviral DNA and impairs viral replication[10,11,12] It has been previously shown, that non-catalytic A3G mutants retain some anti-viral functionality[13,14,15,16,17], indicating the presence of a deamination-independent mode of HIV-1 protection[18,19,20]. One way to determine the effect of oligomerization on A3G function is to examine the behavior of various oligomerizationdeficient mutants Structures of both domains have been obtained[38, 43, 44], which can be used to determine the residues critical to forming the shared interface between A3G monomers when dimers and tetramers are formed. A structural model of A3G dimerized in a ‘head to tail’ orientation (the NTD of one monomer interacting with the CTD of a second monomer) has suggested that some of these residues may be critical to A3G oligomerization and function[46]

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