Disassembly of layer-by-layer films of plasmid DNA and reducible TAT polypeptide

This paper reports the disassembly of layer-by-layer (LbL) films of plasmid DNA and a reducible cationic polypeptide. To utilize a reducing microenvironment of cellular plasma membrane as a potential trigger, LbL films are assembled to contain both DNA and the TAT-based polypeptide (PTAT) with reducible disulfide bonds in the backbone. The assembly and disassembly processes are monitored by goniometry, ellipsometry, and atomic force microscopy (AFM). The structure of the PTAT films is compared with that of non-reducible poly(L-lysine) (PLL) films. Both PTAT and PLL films exhibit exponential growth but with the contact angle alternating between characteristic values. Ellipsometry and AFM show a gradual and complete disassembly of the PTAT but not the PLL films in a 24h period in the reducing environment in vitro. This study suggests a potential of using reducible LbL films for controlled DNA delivery.

Inhibition of HIV-1 TAR RNA-Tat peptide complexation using poly(acrylic acid)

HIV-1 is regulated at the transcriptional level by the interaction of Tat protein with the transactivation responsive region (TAR) RNA, a 59-base stem-loop structure located at the 5'-end of all nascent HIV-1 transcripts. Here, by targeting the Tat peptide, we found that negatively charged poly(acrylic acid) (PAA) had high affinity with Tat peptide and could inhibit the interaction of TAR with Tat. Therefore, PAA could block HIV replication by binding to Tat not to TAR RNA, providing a new thinking for the design of novel anti-HIV drugs.

Exogenous human immunodeficiency virus type-1 Tat protein selectively stimulates a phosphatidylinositol-specific phospholipase C nuclear pathway in the Jurkat T cell line

We investigated the effect of extracellular Tat protein of human immunodeficiency virus-type 1 (HIV-1) on the phosphatidylinositol (PI) cycle, which represents a major signal transduction pathway in lymphoid cells. Recombinant Tat, recombinant HIV-1 p24 and cross-linked anti-CD3 monoclonal antibody (mAb) were added in culture for 1-60 min to Jurkat lymphoblastoid CD4+ T cells. The stimulation of T cell receptor by cross-linked anti-CD3 mAb resulted in a rapid increase of the phosphatidylinositol-specific phospholipase C (PI-PLC) activity in whole cell lysates. On the other hand, Tat protein, either alone or in combination with anti-CD3 mAb, showed little effect on the PI turnover of whole cell extracts. Tat, however, selectively stimulated a nuclear-specific PI-PLC with a peak of activity after 30 min from the addition in culture to Jurkat cells. Interestingly, this time corresponded to that required for the uptake and nuclear localization of recombinant Tat protein, as demonstrated by electron microscope immunocytochemistry experiments with anti-Tat mAb. Moreover, exogenous Tat reached the nucleus of Jurkat cells in a bioactive form, as shown in a HIV-1 long terminal repeat-chloramphenicol acetyl transferase transactivation assay. The specific increase of a nuclear PI-PLC activity was further demonstrated by the ability of Tat to stimulate PI turnover also when added directly to isolated nuclei. As a whole, these data demonstrate that Tat selectively stimulates a nuclear polyphosphoinositide hydrolysis, which appears to be independent of the cellular PI turnover. The relevance of these findings for a better understanding of the biological functions of extracellular Tat is discussed.

Circular dichroism and molecular modeling yield a structure for the complex of human immunodeficiency virus type 1 trans-activation response RNA and the binding region of Tat, the trans-acting transcriptional activator

Transcription in the human immunodeficiency virus type 1 (HIV-1) retrovirus is regulated by binding the viral Tat protein (trans-acting transcriptional activator) to the trans-activation response (TAR) RNA sequence. Here, vacuum UV circular dichroism (VUV-CD) is used to study the structure of TAR and its complex with two peptide fragments that are important for Tat binding to TAR. The VUV-CD spectrum of TAR is typical of A-form RNA and is minimally perturbed when bound to either the short or the long Tat peptide. The CD spectra of the complexes indicate an extended structure in the arginine-rich region of Tat from amino acid residue 47 through residue 58 and a short alpha-helix within the adjacent 59-72 region. Models of TAR and its peptide complexes are constructed to integrate these spectroscopic results with current biochemical data. The model suggests that (i) the arginine-rich 49-58 region is primarily responsible for electrostatic interactions with the phosphates of the RNA, (ii) the arginine side chains can additionally interact with substituent groups of the nucleotide bases to confer base recognition in the complex, (iii) the recognition of uracil-23 in TAR is facilitated by the peptide backbone, and (iv) the glutamine-rich face of an alpha-helix within the 59-72 region pairs to bases UGG at nucleotide positions 31-33 in the TAR loop and thus provides an additional motif in the Tat trans-activating protein to recognize TAR RNA.