Synthesis and biological activity of linear and cyclic enkephalins modified at the Gly3-Phe4 amide bond

As part of our continuing effort to define structure-activity relationships for enkephalin and design enzymatically resistant analogs, we report the synthesis and biological activities of linear and cyclic enkephalin analogs modified at the Gly3-Phe4 amide bond. The partial retro-inverso enkephalin analog Tyr-D-Ala-gGly-(R,S)-mPhe-Leu-NH2 and its cyclic counterpart, Tyr-cyclo[D-A2 bu-gGly-(R,S)-mPhe-Leu-], were synthesized as diastereomeric mixtures using solution methodology. The racemic benzylmalonate allowed the linear analog to be synthesized by fragment coupling at the reversed bond. Cyclization of the second analog was carried out at high concentration, eliminating formation of polymer by the use of an insoluble base. All gem-diaminoalkyl residues were prepared by conversion of peptidyl amides with benzene iodonium bis(trifluoroacetate). Diastereomers of both compounds were separable by reverse phase HPLC but those of the linear compound racemized rapidly under conditions of testing and were therefore tested together. All analogs tested had activities ranging from 6 to 14% of the activity of Leu enkephalin, indicating that the Gly3-Phe4 amide bond is important, though not crucial, for receptor binding.     

Monoclonal antibodies as probes of the alpha-bungarotoxin and cholinergic binding regions of the acetylcholine receptor

We have probed the acetylcholine receptor (AcChR) molecule with six anti-AcChR monoclonal antibodies (mAbs) whose binding to the AcChR is inhibited or blocked by alpha-bungarotoxin (alpha BgTx). mAbs bound with a maximum stoichiometry of either one mAb (387D, 247G) or two mAbs (383C, 572C, 370C, 249E) per AcChR monomer, and the extent to which they inhibited alpha BgTx binding directly correlated with their stoichiometry of binding. The effect of mAbs on the alpha BgTx and cholinergic ligand binding properties of the AcChR molecule defined three major categories of mAbs: those that block alpha BgTx and carbamylcholine (agonist) binding, but do not block d-tubocurarine (antagonist) binding (383C, 572C, 370C and 249E); mAb 387D, which blocks agonist binding and partially blocks alpha BgTx and d-tubocurarine binding; and mAb 247G, which does not affect agonist binding, blocks at most 50% of the alpha BgTx binding sites, and decreases the affinity of the high affinity component of d-tubocurarine binding (Mihovilovic, M., and Richman, D. P. (1984) J. Biol. Chem. 259, 15051-15059). Except for mAb 247G, these mAbs strongly competed with each other for binding to the AcChR. In contrast, mAb 247G blocks about 50% of the binding of all the other mAbs. The results demonstrate the ability of mAbs to stabilize different conformational states of the AcChR and to probe cholinergic epitopes of functional importance. They also indicate the nonequivalence of the two alpha-toxin binding regions of the AcChR molecule and suggest that it is possible to identify epitopes within the alpha BgTx binding region that when bound produce differential effects on the binding of the agonist (carbamylcholine) and the antagonist (d-tubocurarine).     

Tetrahymena contain two distinct and unusual high mobility group (HMG)- like proteins

Previous studies have described the existence of high mobility group (HMG)-like proteins in macronuclei of the ciliated protozoan, Tetrahymena thermophila (Hamana, K., and K. Iwai, 1979, J. Biochem. [Tokyo], 69:1097-1111; Levy-Wilson, B., M. S. Denker, and E. Ito, 1983, Biochemistry, 22:1715-1721). In this report, two of these proteins, LG- 1 and LG-2, have been further characterized. Polyclonal antibodies raised against LG-1 and LG-2 fail to cross react with each other or any other macronuclear polypeptide in immunoblotting analyses. As well, LG- 1 and LG-2 antibodies do not react with calf thymus, chicken, or yeast HMG proteins. Consistent with these results, a 47 amino-terminal sequence of LG-1 has been determined that shows limited homology to both calf thymus HMGs 1 and 2 and HMGs 14 and 17. Two internal sequences of V8 protease-generated peptides from LG-2 have been determined, and these do not share any homology to the LG-1 sequence or any other sequenced HMG proteins. Comparison of the partial sequences of LG-1 and LG-2 with the complete amino acid sequence of the Tetrahymena histone H1 (Wu, M., C. D. Allis, R. Richman, R. G. Cook, and M. A. Gorovsky, 1986, Proc. Natl. Acad. Sci. USA, 83:8674-8678) rules out the possibility that LG-1 and LG-2 are proteolytically derived from H1, the other major macronuclear perchloric acid-soluble protein. Interestingly, however, both LG-1 and LG-2 are efficiently extracted from macronuclei by elutive intercalation (Schroter, H., G. Maier, H. Ponsting, and A. Nordheim, 1985, Embo (Eur. Mol. Biol. Organ.) J., 4:3867-3872), suggesting that both may share yet undetermined properties with HMGs 14 and 17 of higher eukaryotes. Examination of the pattern of LG-1 and LG-2 synthesis during the sexual phase of the life cycle, conjugation, demonstrates that the synthesis of LG-1 and LG-2 is coordinately increased from basal levels during the differentiation of new macronuclei (7-13 h), suggesting that both of these proteins play a role in determining a macronuclear phenotype. However, a specific induction of LG-2 synthesis is detected in early stages of conjugation (meiotic prophase, 1-4 h), leading to maximal synthesis of LG-2 at 3 h. Interestingly, the early induction of LG-2 synthesis closely parallels the hyperphosphorylation of histone H1. Taken together, these data suggest that LG-1 and LG-2 are not strongly related to each other or to higher eukaryotic HMG proteins.(ABSTRACT TRUNCATED AT 400 WORDS)     

Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes

We have examined the phylogenetic distribution of two t-specific markers among representatives of various taxa belonging to the genus Mus. The centromeric TCP-1a marker (a testicular protein variant specific for all t-haplotypes so far studied) has also been apparently detected in several non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor species. By contrast, a t-specific restriction- fragment-length polymorphism allele (RFLP) of the telomeric alpha- globin pseudogene DNA marker alpha-psi-4 was found only in animals belonging to the M. musculus-complex species either bearing genuine t- haplotypes or, like the M. m. bactrianus specimen studied here, likely to do so. This t-specific alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or M. spretus ones. These results suggest the presence of t-haplotypes and of t-specific markers in populations other than those belonging to the M. m. domesticus and M. m. musculus subspecies, implying a possible origin for t-haplotypes prior to the radiation of the most recent offshoot of the Mus genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.      

Rapid and reversible modulation of T4 (CD4) on monocytoid cells by phorbol myristate acetate: effect on HIV susceptibility

The effect of phorbol myristate acetate (PMA) on T4 (CD4) expression by monocytoid cells was studied. Greater than 99% of untreated U937 and HL-60 cells expressed surface T4 as measured with a fluorescence-activated cell sorter. The percentage of T4 positive cells decreased to less than 20% after incubation with PMA (10(-8) M). A decrease was observed within 15 min of PMA exposure, was maximal within 1 hr, and persisted for at least 3 days in the continuous presence of PMA. The susceptibility of untreated and PMA-treated U937 cells to human immunodeficiency virus (HIV) was also studied. Pretreatment of cells with PMA for 18 hr decreased the production of viral RNA and p24 antigen 24 hr after infection. The dose of PMA resulted in a parallel reduction of both T4 expression and infection by HIV. When PMA was washed from cultures and replaced with fresh medium for 48 hr, then T4 expression and the production viral RNA and p24 antigen following infection were restored. These data suggest that pharmacologic manipulation of surface T4 expression may have a potential role in the prevention or treatment of HIV infection.     

T cell recognition of HIV synthetic peptides in a natural infection

Because T cell responses are critical for defense against viral infections, a series of synthetic peptides derived from the predicted sequence for HIV-1 proteins gp41, pg120, gag, and viral polymerase were used to test the T cell proliferative response of HIV-1 seropositive individuals. Of HIV-1-infected donors from various clinical categories 90% (27/30) had sensitized cells that proliferated in response to at least one of 21 HIV peptides tested. Cells from HIV seronegative controls did not proliferate (0/9) in response to these HIV peptides. Individuals with fewer clinical manifestations of HIV-1 disease responded to a greater number of peptides (average for asymptomatic seropositives = 8.1 peptides; AIDS patients averaged 2.0). The number of peptides recognized also correlated with absolute number of CD4+ cells, but not with delayed cutaneous hypersensitivity to a (non-HIV) battery of Ag. However, clinical stage at no time correlated with the response to any particular peptide. Response patterns differed considerably among individuals, and some peptides stimulated proliferation in many (48%) HIV-infected donors (peptides gp41-2 and pol-3), whereas another peptide elicited no T cell response in any donor tested (peptide gp120-8). We have also begun to investigate the basis for individual heterogeneity of T lymphocyte proliferative responses of HIV-infected donors to the 21 HIV synthetic peptides. Peptide structure and HLA class II determinants both influenced patterns of lymphocyte responses. Reactivity correlated with peptide size, the presence of alpha and beta secondary structure and lack of reverse turn potential. Hydropathy and charge had no predictive value. Peptides derived from HIV sequences that vary highly among strains tended to be recognized less frequently. HIV-infected lymphocyte donors were HLA typed to examine the influence of the MHC on T lymphocyte proliferation. Analysis of the frequencies of individuals reacting to specific peptides, when compared to the allele frequencies in the population at large, indicated association of some responses to DR alleles. More DR association was observed with peptides that showed "moderate" reactivity than with those that were "highly" reactive. We suggest that highly reactive peptides are capable of forming a structure closer to an "ideal" T cell epitope that can associate with many DR alleles. In contrast, "moderately" reactive determinants have less favorable structures for interaction, are more limited in their ability to interact and therefore show more restriction to specific class II alleles.     

Motion behavior of nauplii and early copepodid stages of marine planktonic copepods

The goal of this study was to quantify periods of activity andvelocities of late naupliar and early copepodid stages of planktoniccopepods occurring regularly on the southeastern continentalshelf of the USA. We obtained quantitative information on eightspecies, including adult females of Oithona plumifera. All studieswere conducted at food concentrations near or above satiationlevels. Activities ranged from 0.85% (adult females of O.plumifera)to 100% of time (nauplii and copepodids of various calanoidspecies). Motion velocities (excluding escape motion) coveredmore than one order of magnitude: from 0.39 mm s^–1 fornauplii of Temora stylifera to 5.24 mm s^–1 for naupliiof Oncaea mediterranea. Ranges of activities of species rangefrom occasional for early juveniles to adult females of O.plumiferato 100% for the same range of T.stylifera, the latter creatinga feeding current from N III onwards, the former not at all.Of notable interest is Centropages velificatus which moves intermittentlyas a late nauplius, continuously as an early copepodid and intermittentlyas an adult. All observed calanoid late nauplii and copepodidsmove in three dimensions, excluding copepodids of the shelfbreak/oceanicParacalanus aculeatus. The results indicate not only significantdifferences in motion behavior between cyclopoids and calanoids,but also between calanoid species. Yet, some calanoid speciesshow little ontogenetic changes at all.     

Direct comparison of bromodeoxyuridine and Ki-67 labelling indices in human tumours

Direct comparison of bromodeoxyuridine (BrdUrd) and Ki-67 labelling indices was achieved by selecting similar areas from serial sections of human tumours. Fifteen patients were selected who had been administered BrdUrd in vivo and both proliferation markers were assessed by immunohistochemistry. The data show a good correlation between both BrdUrd LI and MIB-1 LI and T_pot (calculated using the flow cytometry derived duration of S phase) and MIB-1 LI. The contribution of BrdUrd LI to growth fraction varied as a function of proliferation characteristics. In tumours with a high LI, the number of DNA synthesizing cells represented half the growth fraction, whilst in tumours with lower LI's (<10%) the ratio of DNA precursor labelled cells as a function of growth fraction fell to between 10% and 20%. T_pot showed a linear correlation with MIB-1/BrdUrd ratio with a slope approaching unity. It was apparent that both intra- and interpatient variation in proliferation index was greater for BrdUrd labelling than for MIB-1 expression.