Poster abstracts
Poster number 15 submitted by Brandon Crowe
Structural insights into human transcription factors utilized by retroviruses to target integration
Brandon L. Crowe (Ohio State Biochemistry Program), Jocelyn Eidahl (College of Pharmacy), Ross Larue (College of Pharmacy), Mamuka Kvaratskhelia (College of Pharmacy), Mark P. Foster (Department of Chemistry and Biochemistry)
Abstract:
Retroviruses must integrate their reverse-transcribed DNA into host chromatin in order to replicate. Sites of retroviral integration are not random and vary by retroviral genera. For example; lentiviruses, such as human immunodeficiency virus type I (HIV-1), selectively target integration to actively transcribed genes, whereas γ-retroviruses, such as murine leukemia virus (MLV), target transcription start sites. This preference is mediated through interactions between retroviral integrases and different host transcription factors. This work provides structural insights into the basis for this differential tethering. Lens epithelium-derived growth factor/p75 (LEDGF/p75) is the human protein that HIV-1 targets to facilitate integration of its retro-transcribed genome. HIV-1 integrase binds LEDGF/p75 through a C-terminal integrase binding domain (IBD), while LEDGF/p75 binds chromatin occurs through a separate PWWP domain named for its conserved Pro-Trp-Trp-Pro motif. We determined the NMR solution structure of the LEDGF/p75 PWWP domain and showed that the protein recognizes both DNA and epigenetic markers for actively transcribed genes (histone H3 with a trimethylated lysine 36, H3K36me3). In contrast, MLV is targeted to chromatin via a different host factor, the bromodomain and extraterminal domain (BET) family epigenetic reader proteins. The BET family contains two N-terminal bromodomains, which bind acetylated lysines that mark histones at transcription start sites, and an extraterminal (ET) domain which normally functions to recruit epigenetic modifying enzymes to chromatin. MLV IN binds the ET domain through the ET binding motif (EBM) located at its extreme C-terminus. We used NMR to determine the solution structure of the Brd4 ET domain in complex with the MLV IN EBM. The structure reveals the formation of a three stranded antiparallel β-sheet, with two strands from the MLV IN EBM and one strand formed by structuring a loop in the ET domain. The structure reveals the formation of a hydrophobic core on one face of the β-sheet and electrostatic interactions on the other face. These studies have provided unique insights into the structural mechanisms retroviruses utilize to target integration to specific sites within human chromatin.
References:
Eidahl, J. O., Crowe, B. L., North, J. A., McKee, C. J., Shkriabai, N., Feng, L., Plumb, M., Graham, R. L., Gorelick, R. J., Hess, S., Poirier, M. G., Foster, M. P., and Kvaratskhelia, M. (2013) Nucleic acids research 41, 3924-3936.
Larue, R. C., Plumb, M. R., Crowe, B. L., Shkriabai, N., Sharma, A., Difiore, J., Malani, N., Aiyer, S. S., Roth, M. J., Bushman, F. D., Foster, M. P., and Kvaratskhelia, M. (2014) Nucleic acids research 42, 4868-81.
Keywords: Retroviruses, Transcription Factors, NMR Solution Structure