A helical chain being the most common secondary structure in biopolymers prefers one-handed (left-or right-handed) screw sense, when chiral moieties are incorporated into the main or side chain through the covalent bond. We here report that an achiral helical peptide prefers the one-handed helical screw sense by noncovalent interaction of its N-terminal amino group with a chiral carboxylic acid. Little is known about such phenomena in peptide systems typical of biopolymers, although it has been reported that synthetic helical polymers bearing carboxyl or amino groups in the repeating units induce the one-handed screw sense by addition of chiral small amines or acids to interact on their polymer side or main chains. 1 In our system, the acid-base interaction occurring in the N-terminal position of the peptide chain will lead to the predominance of one-handed screw sense of the entire peptide chain, namely through domino effect. For our purpose, the following N-deprotected nonapeptide 1 consisting of nonprotein amino acids [R-aminoisobutyric acid (Aib) and R, -dehydrophenylalanine (∆ Z Phe)] was synthesized. 2 Peptide 1 can be expected to generate two "enantiomeric" (leftand right-handed) helices, since Aib and ∆ Z Phe residues are achiral ones and strong inducers for forming a 3 10 -helix. 3 Actually, a helical conformation was evidenced by 1 H NMR spectroscopy on peptide 1 in CDCl 3 . In the NOESY experiment, marked crosspeaks were observed for the N i H-N i+1 H resonances in the segment of Aib(3) to Aib(9), 2 indicating that peptide 1 forms a 3 10 -or R-helix. 4 The solvent dependence on amide NH chemical shifts in CDCl 3 /(CD 3 ) 2 SO mixtures revealed that six NH resonances of ∆ Z Phe(4) to Aib(9) residues are shielded from solvent due to intramolecular hydrogen bonding, 2 of which the pattern corresponds to a 3 10 -helix. The helical conformation was also supported by the amide I absorption bands of its FT-IR spectrum in chloroform: 1660 and 1627 cm -1 , which can be assigned to saturated amino acid and ∆ Z Phe residues in a helical segment, respectively. 5 Furthermore, energy minimization of peptide 1 by the semiempirical molecular orbital method 6 gave a 3 10 -helical conformation ( Figure 1) characterized by 〈φ〉 ) (41.1°, 〈ψ〉 ) (37.6°, and 〈ω〉 ) 180.0°for average values of ∆ Z Phe(2) to ∆ ZPhe(8) residues, and the main-chain energy contour map was severely restricted into right-and left-handed helical regions (φ ) (60 to (40°, ψ ) (60 to (30°). 2 Therefore, peptide 1 having a strong helix-forming tendency forms a 3 10 -helical conformation in chloroform. 7 Peptide 1 could not show any CD signals due to the absence of chiral residues, thus taking both left-and right-handed helices with the same content in an equilibrium state (Figure 2, dotted line). However, intense split CD signals were induced around 282 nm assignable to ∆ Z Phe residues by the addition of enantiomerically pure Boc-L-Pro-OH (Boc ) t-butoxycarbonyl), as shown in Figure 2. The mirror image was obtained by the addition of Boc-D-Pro-OH, th...

The immediately-early response gene 5 (IER5) has been reported to be induced by γ-ray irradiation and to play a role in the induction of cell death caused by radiation. We previously identified IER5 as one of the 2,3,4-tribromo-3-methyl-1-phenylphospholane 1-oxide (TMPP)-induced transcriptional responses in AML cells, using microarrays that encompassed the entire human genome. However, the biochemical pathway and mechanisms of IER5 function in regulation of the cell cycle remain unclear. In this study, we investigated the involvement of IER5 in the cell cycle and in cell proliferation of acute myeloid leukemia (AML) cells. We found that the over-expression of IER5 in AML cell lines and in AML-derived ALDHhi (High Aldehyde Dehydrogenase activity)/CD34+ cells inhibited their proliferation compared to control cells, through induction of G2/M cell cycle arrest and a decrease in Cdc25B expression. Moreover, the over-expression of IER5 reduced colony formation of AML-derived ALDHhi/CD34+ cells due to a decrease in Cdc25B expression. In addition, over-expression of Cdc25B restored TMPP inhibitory effects on colony formation in IER5-suppressed AML-derived ALDHhi/CD34+ cells. Furthermore, the IER5 reduced Cdc25B mRNA expression through direct binding to Cdc25B promoter and mediated its transcriptional attenuation through NF-YB and p300 transcriptinal factors. In summary, we found that transcriptional repression mediated by IER5 regulates Cdc25B expression levels via the release of NF-YB and p300 in AML-derived ALDHhi/CD34+ cells, resulting in inhibition of AML progenitor cell proliferation through modulation of cell cycle. Thus, the induction of IER5 expression represents an attractive target for AML therapy.

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An x-ray crystallographic analysis was carried out for Boc-(Aib-DeltaZPhe)4-Aib-OMe (1: Boc = t-butoxycarbonyl; Aib = alpha-aminoisobutyric acid; DeltaZPhe = Z-alpha,beta-didehydrophenylalanine) to provide the precise conformational parameters of the octapeptide segment -(Aib-DeltaZPhe)4-. Peptide 1 adopted a typical 3(10)-helical conformation characterized by = +/-55.8 degrees (50 degrees -65 degrees), = +/-26.7 degrees (15 degrees -45 degrees), and = +/-179.5 degrees (168 degrees -188 degrees) for the average values of the -(Aib-DeltaZPhe)4- segment (the range of the eight values). The 3(10)-helix contains 3.1 residues per turn, being close to the "perfect 3(10)-helix" characterized by 3.0 residues per turn. NMR and Fourier transform infrared (FTIR) spectroscopy revealed that the 3(10)-helical conformation at the atomic resolution is essentially maintained in solution. Energy minimization of peptide 1 by semiempirical molecular orbital calculation converged to a 3(10)-helical conformation similar to the x-ray crystallographic 3(10)-helix. The preference for a 3(10)-helix in the -(Aib-DeltaZPhe)4- segment is ascribed to strong inducers of the 3(10)-helix inherent in Aib and DeltaZPhe residues-in particular, the Aib residues tend to stabilize a 3(10)-helix more effectively. Therefore, the -(Aib-DeltaZPhe)4- segment is useful to rationally design an optically inactive 3(10)-helical backbone, which will be of great importance to provide novel insights into noncovalent and covalent chiral interactions of a helical peptide with a chiral molecule.

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Quantitative evaluation of Förster-type fluorescence resonance energy transfer (FRET) was undertaken by statistical investigations on perylene-cored anthracene dendrimers.

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