APOBEC3G (A3G), an enzyme expressed in primates with the potential to inhibit human immunodeﬁciency virus type 1 (HIV-1) infectivity, is a single-stranded DNA (ssDNA) deoxycytidine deaminase with two domains, a catalytically active, weakly ssDNA binding C-terminal domain (CTD) and a catalytically inactive, strongly ssDNA binding N-terminal domain (NTD). Using optical tweezers, we measure A3G binding a single, long ssDNA substrate under various applied forces to characterize the binding interaction. A3G binds ssDNA in multiple steps and in two distinct conformations, distinguished by degree of ssDNA contraction. A3G stabilizes formation of ssDNA loops, an ability inhibited by A3G oligomerization. Our data suggests A3G securely binds ssDNA through the NTD, while the CTD samples and potentially deaminates the substrate. Oligomerization of A3G stabilizes ssDNA binding but inhibits the CTD's search function. These processes explain A3G's ability to efficiently deaminate numerous sites across a 10,000 base viral genome during the reverse transcription process.
Source data files have been supplied for figures 2, 2 supplement, 3, 4, and 5. Additionally, custom written Matlab and Lab windows code is supplied with this manuscript.
- Michael Morse
- Ioulia Rouzina
- Mark C Williams
- Yuqing Feng
- Linda Chelico
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Maria Spies, University of Iowa, United States
© 2019, Morse et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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