Structural Basis of Lysine-Acetylated HIV-1 Tat Recognition by PCAF Bromodomain

Abstract

The human immunodeficiency virus type 1 (HIV-1) trans-activator protein Tat stimulates transcription of the integrated HIV-1 genome and promotes viral replication in infected cells. Tat transactivation activity is dependent on lysine acetylation and its association with nuclear histone acetyltransferases p300/CBP (CREB binding protein) and p300/CBP-associated factor (PCAF). Here, we show that the bromodomain of PCAF binds specifically to HIV-1 Tat acetylated at lysine 50 and that this interaction competes effectively against HIV-1 TAR RNA binding to the lysine-acetylated Tat. The three-dimensional solution structure of the PCAF bromodomain in complex with a lysine 50-acetylated Tat peptide together with biochemical analyses provides the structural basis for the specificity of this molecular recognition and reveals insights into the differences in ligand selectivity of bromodomains.

The Werner Syndrome Helicase Is a Cofactor for HIV-1 Long Terminal Repeat Transactivation and Retroviral Replication

“…NF-B and SP1) that synergize with the transactivator protein, Tat, bound to TAR-RNA, to promote retroviral gene expression in HIV-1-infected tissues, macrophages/monocytes, and CD4 ϩ T-lymphocytes (6 -17). The mechanism by which Tat/TAR-RNA complexes regulate transcription from the HIV-1 LTR involves the concerted recruitment of a plethora of cellular factors, including p300/CREB-binding protein (p300/CBP) (18 -25), [26][27][28][29][30], P-TEFb (30 -33), SET7/SET9 methyltransferases (34), SIRT1 (35), the Brm component of the SWI/SNF chromatin-remodeling com- …”

HIV-1 Tat Interactions with p300 and PCAF Transcriptional Coactivators Inhibit Histone Acetylation and Neurotrophin Signaling through CREB

“…Acetylation of lysines Lys 50 / Lys 51 by p300/CBP prevents binding of acetylated Tat to TAR-RNA and is proposed to enhance HIV-1 transcriptional activation through "recycling" of the viral trans-activator (56,57); Lys 50 acetylation also creates a new binding site for PCAF and facilitates the formation of a PCAF-Tat-PTEF-b ternary complex (57). The bromodomain of PCAF specifically binds Lys 50 -acetylated Tat, and this interaction has been demonstrated to prevent Lys 50 -acetylated Tat from binding TAR-RNA (55,57). Recruitment of p300/CBP and PCAF by Tat to the HIV-1 long terminal repeat is essential for viral replication and facilitates HIV-1 gene expression when the provirus integrates in transcriptionally silent regions of the genome (54,56,57,59,60).…”

Thermodynamic analysis of acetylation-dependent Pb1 bromodomain–histone H3 interactions

“…A comparison of the loop regions of Brg1, P/CAF, and Gcn5 shows significant conformational differences to accommodate peptide binding [37,39,41]. Furthermore, the BrD-acetyl-lysine interface in the hydrophobic pocket is further maximized by contacting amino acids that flank the acetyl-lysine.…”

“…The difference in each case likely is a result of the larger solvent-exposed surface area in the nonspecific complex, which does not form a tight fit at the macromolecular interface, compared with the specifically bound complex. The site-specific binding of BrD3 to histone H3 displaying AcK9 may be due to multiple features inherent to an induced fit mechanism, including the folding of the BrD around the acetyl-lysine and dehydration of the binding interface that encompasses one or more amino acids to the amino and carboxy sides of the acetyl-lysine.A comparison of the loop regions of Brg1, P/CAF, and Gcn5 shows significant conformational differences to accommodate peptide binding [37,39,41]. Furthermore, the BrD-acetyl-lysine interface in the hydrophobic pocket is further maximized by contacting amino acids that flank the acetyl-lysine.…”