A structural study of model peptides derived from HIV‐1 integrase central domain

Abstract

The HIV-1 integrase (IN) catalyzes the integration of viral DNA in the human genome. In vitro the enzyme displays an equilibrium of monomers, dimers, tetramers and larger oligomers. However, its functional oligomeric form in vivo is not known. We report a study of the auto-associative properties of three peptides denoted K156, E156 and E159. These derive from the alpha4 helix of the IN catalytic core. The alpha4 helix is an amphipatic helix exposed at the surface of the protein and could be involved in the oligomerization process through its hydrophobic face. The peptides were obtained from the replacement of several amino acid residues by more helicogenic ones in the alpha4 helix peptide. K156 carries the basic residues Lys156 and Lys159, which have been shown important for the binding of IN to viral DNA. In E156 and E159 they are replaced with the acidic residue Glu. A fourth peptide K(E)156 obtained from the replacement of hydrophobic residues with Glu in K156 in order to abolish the auto-associative properties is used as a negative control. The capacity shown by peptides for alpha-helical formation is demonstrated by circular dichroism (CD) analysis performed in aqueous solution and in aqueous trifluoroethanol (TFE) mixtures. Both electrospray ionization mass spectrometry (ESI-MS) and glutaraldehyde chemical cross-linking show that peptides adopt different solvent-dependent equilibriums of monomers, dimers, trimers and tetramers. Oligomerization of peptides in aqueous solution is related to their ability to form helical structures. Addition of a small amount of TFE (<10%) stimulates helix stabilization and the interhelical hydrophobic contacts. Higher amounts of TFE alter the hydrophobic contacts and disrupt the oligomeric species. In addition to hydrophobic interactions, the patterns indicate that the biologically important Lys156 and Lys159 residues also participate in helix association. K(E)156 despite its ability to adopt a helical structure is unable to associate into oligomers, demonstrating the importance of hydrophobic contacts for oligomerization. Thus, the designed peptides provide us information on the functional properties of the alpha4 IN that seems to hold a dual role in DNA recognition and protein oligomerization.

On the synthesis of cyclodextrin–peptide conjugates by the Huisgen reaction

“…We also synthesized the 25‐mer peptide 6 containing the same spacer. This peptide is known to form an α‐helix, as shown by our previous studies . Once again, bis‐labeling of the CDX 2 with 6 was successful, affording the expected bis‐derivative 14 in a 53% yield (Figures and , Table ).…”

“…These scaffolds can have very different structures, such as porphyrins , cyclopeptides , or polyresorcinols . We have previously developed the idea of growing helical coiled‐coil structure peptides by attaching peptides to calixarenes . These peptides, which are 20–25 amino acids in length, show a propensity to form dimers, trimers, and even tetramers, as detected by mass spectrometry .…”

Specificity of LTR DNA recognition by a peptide mimicking the HIV-1 integrase α4 helix

“…Lys156, Lys159 and Asn155 have been further shown to interact with the L731–988 derivative (66) and 5CITEP (67), two IN inhibitors supposed to interact at the DNA–protein interface. On another hand the CSD exhibited by Leu161 could be attributed to changes caused by interactions occurring with residues in close proximity or by the dissociation of K156 multimers stabilized by hydrophobic residues (68).

Figure 5.CSDs for the αHs ( A ) and NHs ( B ) of K156 bound to LTR34 at a DNA:peptide ratio of 1:2.

…”