Abstract
Super elongation complex (SEC) is a positive regulator of RNA polymerase II, which is required for HIV-1 proviral transcription. AFF1/4 is the scaffold protein that recruits other components of SEC and forms dimer depending on its THD domain (TPRL with Handle Region Dimerization Domain). Here we report the crystal structure of the human AFF4-THD at the resolution of 2.4 Å. The α4, α5, and α6 of one AFF4-THD mediate the formation of a dimer and pack tightly against the equivalent part of the second molecule in the dimer of AFF-THD. Mutagenesis analysis revealed that single mutations of either Phe1014 or Tyr1096 of AFF4 to alanine impair the formation of the AFF4 dimer. In addition, transactivation assay also indicated that Phe1014 and Tyr1096 of AFF4 are critical to the transactivation activity of AFF4. Interestingly, the corresponding residues Phe1063 and Tyr1145 in AFF1 have an effect on the transactivation of HIV-1 provirus. However, such mutations of AFF1/4 have no effect on the interaction of AFF1/4 with other subunits of the SEC. Together, our data demonstrated that the dimerization of AFF1/4 is essential to transactivation of HIV-1 provirus.
Highlights
Acquired immune deficiency syndrome is a global threat caused by the human immunodeficiency virus-1 (HIV-1)[1]
The α1 helix, with a highly dynamic N-terminal loop standing out of the ring, packs along α2 in the manner of a helix–turn–helix fold (Fig. 1a). Those helices mentioned above constitute the tetratrico peptide repeat like domain (TPRL) (Fig. 1a). α5 and the N-terminal portion of α6 (Gln1087 to Asn1102) sticks out of the TPRL domain, which resembles a handle of TPRL domain and is referred to as Handle Region (HR) hereafter (Fig. 1a)
Compared with the tetratrico peptide repeats (TPRs) of Afadin, Apc[5], DHR81, and 14–3–3 β, we found that α2 and α4 of AFF4TPRL match well with Helix A, while α1, α3, and α6 are superimposable onto Helix B (Fig. 2a, Supplementary Fig. S4)
Summary
Acquired immune deficiency syndrome is a global threat caused by the human immunodeficiency virus-1 (HIV-1)[1]. The major problem of developing an HIV-1 cure lies in the ability of the virus to persist in patients as latent provirus, which had integrated itself into the genome of CD4+ cells. To thoroughly clear HIV-1, a therapeutic approach known as “shock and kill” is studied intensively. This strategy aims to first reactivate the latent provirus, suppress the transcription of reactivated virus by ARTs while eliminating the exposed virus-producing cells[3]. An opposite approach called “block-and-lock” provides an alternative for a functional cure of HIV, in which agents are used to establish a state of deep latency that prevents provirus from reactivation[3,4]
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