We have recently derived from human fetal blood (25 wks) a series of cloned cell lines that were selected for their ability to kill the conventional natural killer (NK) target cell K562. It was found that a fraction of these clones express CD3 proteins but not the monomorphic Ti alpha beta determinant recognized by WT31 antibody. One interleukin-2-dependent CD3+ WT31- clone, termed F6C7, was used for immunization of mice to generate monoclonal antibodies directed at a potentially novel recognition receptor. It was shown that F6C7 cells, which transcribe Ti beta but not Ti alpha genes, surface-express a clonotypic structure, termed NKFi. Immunoprecipitations performed with anti-NKFi monoclonal antibody (mAb) indicated that the corresponding molecule is resolved in SDS-polyacrylamide gel electrophoresis (PAGE) as a single band of relative molecular mass approximately 85,000 (Mr approximately 85K). After reduction, a major band was detected at 44K and a faint band was present at 41K. The present study was designed to characterize this structure. It was found that NKFi represents either two 44K disulphide-linked gamma (TCR) chains, or possibly one gamma chain associated to an additional undetected molecule, and that the 41K material corresponds to a partially glycosylated fraction of the gamma protein. Anti-NKFi mAb both induces a specific autocrine proliferative response and blocks cytotoxic function, demonstrating that gamma chains serve as functional receptor structures on subpopulations of normal human lymphocytes.

EAA26 (VESMNEELKKIIAQVRAQAEHLKTAY) is a better inhibitor of human immunodeficiency virus, type1, integrase than its parent Lys-159, reproducing the enzyme segment 147-175 with a nonpolar-polar/charged residue periodicity defined by four helical heptads (abcdefg) prone to collapse into a coiled-coil. Circular dichroism, nuclear magnetic resonance, sedimentation equilibrium, and chemical cross-linking were used to analyze EAA26 in various trifluoroethanol/H 2 O mixtures. In pure water the helix content is weak but increases regularly up to 50 -60% trifluoroethanol. In contrast the multimerization follows a bell-shaped curve with monomers in pure water, tetramers at 10% trifluoroethanol, and dimers at 40% trifluoroethanol. All suggest that interhelical interactions between apolar side chains are required for the coiled-coil formation of EAA26 and subsist at medium trifluoroethanol concentration. The N H temperature coefficients measured by nuclear magnetic resonance show that at low trifluoroethanol concentration the amide groups buried in the hydrophobic interior of four ␣-helix bundles are weakly accessible to trifluoroethanol and are only weakly subject to its hydrogen bond strengthening effect. The increased accessibility of trifluoroethanol to buried amide groups at higher trifluoroethanol concentration entails the reduction of the hydrophobic interactions and the conversion of helix tetramers into helix dimers, the latter displaying a smaller hydrophobic interface. The better inhibitory activity of EAA26 compared with Lys-159 could arise from its better propensity to form a helix bundle structure with the biologically important helical part of the 147-175 segment in integrase.The well defined conformational properties exhibited by many peptides in solution have led to their use as models for protein folding and stability but also for the design of peptide inhibitors of enzymes (1-3). The model peptides are either artificial (4 -6) or may reproduce protein segments (7-13). When they have defined conformations, the peptides can provide useful information on the relationships between local interactions, secondary structures, and tertiary structures (14 -17).We have previously tested the hypothesis that synthetic peptides reproducing amphipathic helical segments of enzymes may interact with these segments and interfere with the catalytic properties. Examples concern topoisomerase II (10, 11), an enzyme involved in the maintenance of DNA topology, and also retroviral integrase (IN) 1 (12, 13) that catalyzes the integration of viral DNA into host cellular DNA (two recent reviews, Refs. 18 and 19). IN has no cellular counterpart and can be therefore considered as a specific target for development of anti-HIV therapy (20). In an earlier study, we have reported (13) that Lys-159, a peptide corresponding to the 147-175 segment of HIV-1 IN, inhibited the integration catalyzed by IN, most likely through specific binding to its counterpart in the protein. Such a specific binding was plausible since in the crystal struct...

Monospecific antibodies were raised against a synthetic peptide K159 (SQGVVESMNKELKKIIGQVRDQAEHLKTA) reproducing the segment 147–175 of HIV‐1 integrase (IN). Synthesis of substituted and truncated analogs of K159 led us to identify the functional epitope reacting with antibodies within the C‐terminal portion 163–175 of K159. Conformational studies combining secondary structure predictions, CD and NMR spectroscopy together with ELISA assays, showed that the greater is the propensity of the epitope for helix formation the higher is the recognition by anti‐K159. Both the antibodies and the antigenic peptide K159 exhibited inhibitory activities against IN. In contrast, neither P159, a Pro‐containing analog of K159 that presents a kink around proline but with intact epitope conformation, nor the truncated analogs encompassing the epitope, were inhibitors of IN. While the activity of antibodies is restricted to recognition of the sole epitope portion, that of the antigenic K159 likely requires interactions of the peptide with the whole 147–175 segment in the protein [Sourgen F., Maroun, R.G., Frère, V., Bouziane, A., Auclair, C., Troalen, F. & Fermandjian, S. (1996) Eur. J. Biochem. 240, 765–773 ]. Actually, of all tested peptides only K159 was found to fulfill conditions of minimal number of helical heptads to achieve the formation of a stable coiled‐coil structure with the IN 147–175 segment. The binding of antibodies and of the antigenic peptide to this segment of IN hampers the binding of IN to its DNA substrates in filter‐binding assays. This appears to be the main effect leading to inhibition of integration. Quantitative analysis of filter‐binding assay curves indicates that two antibody molecules react with IN implying that the enzyme is dimeric within these experimental conditions. Together, present data provide an insight into the structure–function relationship for the 147–175 peptide domain of the enzyme. They also strongly suggest that the functional enzyme is dimeric. Results could help to assess models for binding of peptide fragments to IN and to develop stronger inhibitors. Moreover, K159 antibodies when expressed in vivo might exhibit useful inhibitory properties.

In an attempt to further study various fragments of free and combined forms of hCG beta present in biological fluids, we performed one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by Western immunoblotting using antipeptide antibodies directed to the hCG beta-(111-116) portion (monoclonal antibody FB12) antiserum to the hCG beta(8-16) portion or antiserum which was specific for fragments ending at residue 47. Results observed in a crude preparation of urinary hCG demonstrated that in addition to the carboxyl-terminal part of the reduced hCG beta nicked subunit (beta NS) [hCG beta-(48-145)], three other fragments of mol wt 18,000 (F1), 16,500 (F2), and 12,000 (F3) were detectable after cleavage of disulfide bonds. Both the immunoreactivity pattern and peptide sequencing revealed that the F1 fragment was constituted of the hCG beta-(1-47) sequence, whereas the F2 fragment comprised the 6-47 portion. We then studied the beta NS in urine from either pregnant women or four patients with choriocarcinomas. Results showed that both hCG and the free beta-subunit contained beta NS. Furthermore, free hCG beta present in those urine samples appeared to be extensively, if not totally, nicked. Results observed in urine were confirmed using separation of hCG from its beta-subunit by a two-step chromatography procedure, identification of hCG and hCG beta immunoreactive peaks by specific monoclonal immunoradiometric assay, and analysis of resulting preparations by one-dimensional electrophoresis under reducing conditions, followed by Western immunoblotting with FB12. This latter protocol was also used to investigate the presence of beta NS in sera of four patients with choriocarcinoma tumors. In those sera, hCG appeared to be nicked. This study demonstrates that the beta-subunit of hCG is modified by multiple fragmentations.

In a previous paper, we reported on the structural propertics of a 35-residue pcptide corresponding to a modified basic subdomain (bSD) of the basic zipper protein u-Jun (residues 252-281 ) as deterrnincd by combined use of 'H-NMR, circular dichroisrn (CD) and Fourier transform infrared ( F T I R ) spectroscopies [Krcbs, D., Dahmani, B., El Antri, S., Monnot, M., Convert, O., Mauffret, O., Troalen, 1;. 8r Fcrmandjian, S. (1995) Eur: J. Binchem. 231, 370-3801. The fragmenls N P anci CP (the N-terminitl rcsidues 1-19 and C-terminal residues 16-35 of bSD, rcspectivcly) proved to be particularly useful for the assignment of the 'H-NMR spectra of the full-length bSD, which has bccn achievcd coniplctely in aqueous solution and partially in tritluoroethanol. Here, we report on lhc structural properties of NP and CP in aqueous solution and under varying H,O/tritluoroethanol conditions, again using 'H-NMK, C' D and FT-IR experiments. Both CD and FT-TR rcsults establishcd thal the fragments are weakly structured i n aqueous solution. Addition of trifluoroethanol to aqueous solutions of the peptidcs prciduced their stabilization into helix, following a profile sigmoidal for N P and nearly linear for CP. Quantitative NOES, secondary Ha chemical shifts, NH temperature coefficients and coupling conslants for thc peplidcs in aqueous solutions provided indications for weak hclix features (nuscent helices) manifested within two sites (continuous dNN NOES) in both NP and CP. For each peptide, an excellent agrcemen( was observed between experiments and predictions with the AGADIR program fur the location of these nuscent helices in the sequences. Trifluoroethanol provoked both the a-helix stabilization within these sitcs anci the cxhelix propagation to adjacent amino acid residues.Finally, our results reflected the high flexibility and hclix potential of the NP and CP fragments, thesc two propertics seeming crucial for the accomodation of c-J~iti to its specific DNA targets. The rcsults dzinonstrated also the fragmentation's benefits in dissecting a protein or a complex peptide into smaller fragments and analyzing their structure individually.