Being stimulated by the insights from model studies that (i) the intimate combination of hydrogen-bonding pairing and aromatic stacking interactions is important for the specific binding of guanine base by peptide and (ii) the π-π stacking force of Trp is significantly strengthened by the guanine N7-methylation (m7G), this research project was started, because (a) the mRNA cap structure is characterized by the existence of m7G and (b) an eukaryotic initiation factor-4E (eIF-4E), a protein which specifically recognizes the mRNA cap structure and opens the protein biosynthesis, contains 8 Trp residues irrespective of its relatively low molecular weight of about 25 kDa. In order to prepare the sufficient amount of sample for carrying out the analysis of the recognition mechanism of mRNA cap structure by eIF-4E at the atomic level, firstly, the expression of human eIF-4E gene in Escherichia coli was attempted. An artificial gene encoding for human eIF-4E was chemically synthesized and succeeded in the expression with two different forms, i.e., as a fusion protein with human growth hormone and a direct expression of soluble protein. The isolation of eIF-4E and its purification procedure using the m7GTP affinity chromatography were accomplished. It was shown by spectroscopic methods that the recombinant eIF-4E exhibits essentially the same tertiary structure as the native one and the binding ability with mRNA cap analog was identical with each other. In order to analyze the functional amino acid residues which are essential for specific recognition of mRNA cap structure, next a series of eIF-4E mutants were prepared by the site-directed mutagenesis, and His37, His200, Trp102 and Glu103 were suggested to be important for binding of mRNA cap structure, as judged from comparison of the binding abilities of respective mutants with a m7GTP affinity column. Since the crystals of recombinant eIF-4E-m7GTP complex suitable for X-ray crystallography are now in preparation, the detailed interaction mode between them will be opened in near future.
The mammalian spermatogenic pathway is a complex process that involves the mitotic proliferation of spermatogonia, the meiotic division of spermatocytes, chromosomal condensation, the production of sperm-specific proteins, and the morphogenic differentiation of spermatids to mature sperm. Elucidating the molecular basis of mammalian spermatogenesis is of great importance, not only because spermatogenesis is a fundamental biological event in the organism but because understanding of this mechanism could lead to the development of new therapeutics to overcome certain genetic diseases. Numerous cytological studies have described, in detail, the dramatic morphological changes of the differentiating spermatogenic cells, however, the molecular basis for many of these steps has yet to be elucidated. What has hampered the progress of such research is the lack of suitable experimental systems. Establishing cultured cell lines of testicular cells has been attempted for many times without much success. We have studied the molecular basis for the mammalian spermatogenic pathway, making use of two unique systems ; cell-free transcription reactions in nuclear extracts of animal organs and primary culture of rat testicular cells. Expression of a variety of genes is activated or inactivated as the spermatogenic pathway progresses. The isozyme for glycolytic enzyme phosphoglycerate kinase (PGK) changes in spermatogenic cells from somatic-type PGK-1 to sperm-type PGK-2. We showed that the PGK isozyme switch occurs at the mRNA level during the pachytene spermatocyte stage, suggesting that Pgk-1 transcription ceases and Pgk-2 transcription is instead induced at this stage. The mechanism of the Pgk transcription switch was then investigated by cell-free transcription and DNA transfection experiments. We found that the activation of Pgk-2 transcription in the testis is caused mainly by an Ets family transcription factor named TAP-1, and that the same protein is likely to be involved in the inactivation of the Pgk-1 gene during spermatogenesis. Silencer-like negative regulatory DNA sequences and proteins bound to them seemed to be responsible for the repression of Pgk-1 transcription in the somatic tissues. Throughout the spermatogenic pathway, spermatogenic cells remain in close contact with each other and with somatic Sertoli cells in the seminiferous tubules. Although a number of reports have suggested that Sertoli cells play an important role in spermatogenesis, little is known about the mechanism by which these cells influence spermatogenic cell differentiation. When testicular cells from 20-day-old rats were cultured, at the time when the induction of Pgk-2 gene expression is just beginning, the amount of PGK-2 mRNA increased and that of PGK-1 mRNA decreased in spermatogenic cells during culture. This indicated that cultured spermatogenic cells advanced in their development across the pachytene stage. In this culture, spermatogenic cells are co-cultured with somatic cells that mostly consist of Sertoli cells. We thus studied the interaction between spermatogenic and Sertoli cells in this culture system. The PGK mRNA switch was not observed when the two cell types were co-cultured without direct contact. Furthermore, we found that a significant proportion of spermatogenic cells died by apoptosis during culture, and that Sertoli cells phagocytosed and digested degenerating spermatogenic cells. These results indicate that Sertoli cells participate both in the differentiation of spermatogenic cells and in the exclusion of degenerating spermatogenic cells, by directly attaching to those cells.
Studies on host-guest molecular recognition at membrane surfaces, which involves changes in the membrane potential, are described. A special focus was placed on basic approaches for the potentiometric discrimination of organic guests in liquid membrane systems. The following modes of host-guest interaction have been exploited for the structure discrimination based on membrane potential changes. (i) Electrostatic interaction by protonated polyamine hosts to discriminate organic anion guests. (ii) Complementary base pairing by hosts having a cytosine residue to discriminate nucleotide guests bearing guanine and adenine bases. (iii) Inclusion of nonpolar moieties of guests by a calix  arene hexaester or a β-cyclodextrin derivative to discriminate amine guests having different steric structures. Some characteristic aspects of host-guest molecular recognition at membrane surfaces are discussed in comparison with those in homogeneous solutions.
Tilivalline (1a), a metabolite isolated from Klebsiella pneumoniae var. oxytoca, belongs to a group of pyrrolo [2, 1-c] [1, 4] benzodiazepines, a characteristic skeleton of anthramycin-type antitumor antibiotics. We have accomplished a completely stereoselective, efficient and convenient synthesis of 1a utilizing a new Mannich type intramolecular cyclization as a key step. Further, a computational chemical analysis clarified the effect of zinc chloride on the high stereoselectivity in the tilivalline synthesis. To aim both the extension of the scope of the new Mannich type intramolecular cyclization and the studies on the structure-biological activity relationship, we further extended the method to the synthesis of tilivalline derivatives and 2-(3'-indolyl)-1, 4-benzodiazepines (50). Investigation on the cytotoxicity of 1a and its analogs has revealed that 1a shows the strong cytotoxicity toward mouse leukemia L 1210 cells and the replacement of the indole function of 1a with cyano one increases the cytotoxicity of 1a about 100 times (IC50=0.05 μg/ml).
The 2-oxazolone proved to be highly potent as a versatile building block for the stereodefined construction of 2-amino alcohols, for which the synthetic strategy involving a key step, the preparation of chiral synthons by the stereoselective addition of easily replaceable substituents such as Br, PhSe and MeO groups to the olefinic moiety of the 2-oxazolone skeleton followed by the straightforward manipulation is described. By this methodology, a variety of unusual hydroxy amino acids of bioactive peptides such as pepstatine, bestatine, amastatine have been easily synthesized in optically pure forms.
Averaged blood glucose levels were 400 mg/dl in nonfasted mice, and 250 mg/dl in fasted mice in 4 weeks after injection with streptozotocin (STZ, 150 mg/kg, i.v.). These mice were used for experiments. Hypoglycemic effects of hot water extracts (W) from Folium Mori (Mulberry leaves, Morus alba L., China and Japan) or Cortex Mori Radicis (Morus alba L., China) were observed in fasted and nonfasted STZ-induced diabetic mice at a single dose of 200 mg/kg (i.p.). The W from Folium Mori exhibited most potent hypoglycemic effects. The most potent fractions of Folium Mori and Cortex Mori Radicis were ethanol-insoluble extracts (A2). These A2 fractions demonstrated a fall in blood glucose levels of 24.6±6.0% and 60.5±9.1% at nonfasted STZ-mice, and 81.4±7.9% and 77.3±5.8% at fasted STZ-mice, respectively. The increase in glucose uptake was a mechanism of hypoglycemic actions by W and A2 of Folium Mori.