Selective assembly on a surface of supramolecular aggregates with controlled size and shape

The realization of molecule-based miniature devices with advanced functions requires the development of new and efficient approaches for combining molecular building blocks into desired functional structures, ideally with these structures supported on suitable substrates 1-4. Supramolecular aggregation occurs spontaneously and can lead to controlled structures if selective and directional non-covalent interactions are exploited. But such selective supramolecular assembly has yielded almost exclusively crystals or dissolved structures 5; the self-assembly of absorbed molecules into larger structures 6-8, in contrast, has not yet been directed by controlling selective intermolecular interactions. Here we report the formation of surface-supported supramolecular structures whose size and aggregation pattern are rationally controlled by tuning the non-covalent interactions between individual absorbed molecules. Using low-temperature scanning tunnelling microscopy, we show that substituted porphyrin molecules adsorbed on a gold surface form monomers, trimers, tetramers or extended wire-like structures. We find that each structure corresponds in a predictable fashion to the geometric and chemical nature of the porphyrin substituents that mediate the interactions between individual adsorbed molecules. Our findings suggest that careful placement of functional groups that are able to participate in directed non-covalent interactions will allow the rational design and construction of a wide range of supramolecular architectures absorbed to surfaces.

The product of ras is a GTPase and the T24 oncogenic mutant is deficient in this activity

Ha-ras is a member of a multigene family in man which encode highly related proteins of 189 amino acids (p21). In vitro, ras proteins bind GTP, and p21 mutants with treonine at position 59 autophosphorylate at that residue. Mutation (at amino acids 12 or 61) and elevated expression of ras genes result in cell transformation in culture, and are also observed in many types of human tumours. Normal and mutant transforming ras proteins show no differences in localization, lipidation or GTP binding. However, mutations at position 12 in recombinant (Thr 59) p21 molecules were observed to affect autophosphorylation. We have expressed the full-length normal and T24 transforming (Gly----Val at position 12) Ha-ras proteins in Escherichia coli and have purified them to homogeneity (ref. 19 and M.G. et al., in preparation); these proteins bound GTP with approximately molar stoichiometry and with an affinity comparable to partially purified mammalian proteins. Microinjection of the T24 protein into quiescent rodent fibroblasts resulted in a rapid alteration in cell morphology, stimulation of DNA synthesis and cell division; in contrast, little response was observed with the normal protein. We now report that the normal ras protein has an intrinsic GTPase activity, yielding GDP and Pi. In contrast, the T24 transforming protein is reduced 10-fold in this activity. We suggest that this deficiency in GTPase is the probable cause for the transforming phenotype of the T24 protein.

Molecular evolution of vertebrate visual pigments

Dramatic improvement of our understanding of the genetic basis of vision was brought by the molecular characterization of the bovine rhodopsin gene and the human rhodopsin and color opsin genes (Nathans and Hogness, 1983; Nathans et al., 1984, 1986a,b). The availability of cDNA clones from these studies has facilitated the isolation of retinal and nonretinal opsin genes and cDNA clones from a large variety of species. Today, the number of genomic and cDNA clones of opsin genes isolated from different vertebrate species exceeds 100 and is increasing rapidly. The opsin gene sequences reveal the importance of the origin and differentiation of various opsins and visual pigments. To understand the molecular genetic basis of spectral tuning of visual pigments, it is essential to establish correlations between a series of the sequences of visual pigments and their lambda(max) values. The potentially important amino acid changes identified in this way have to be tested whether they are in fact responsible for the lambda(max)-shifts using site-directed mutagenesis and cultured cells. A major goal of molecular evolutionary genetics is to understand the molecular mechanisms involved in functional adaptations of organisms to different environments, including the mechanisms of the regulation of the spectral absorption. Therefore, both molecular evolutionary analyses of visual pigments and vision science have an important common goal.

Codon and amino-acid specificities of a transfer RNA are both converted by a single post-transcriptional modification

An Escherichia coli isoleucine transfer RNA specific for the codon AUA (tRNA(2Ile) or tRNA(minorIle] has a novel modified nucleoside, lysidine in the first position of the anticodon (position 34), which is essential for the specific recognition of the codon AUA. We isolated the gene for tRNA(2Ile) (ileX) and found that the anticodon is CAT, which is characteristic of the methionine tRNA gene. Replacement of L(34) of tRNA(2Ile) molecule enzymatically with unmodified C(34) resulted in a marked reduction of the isoleucine-accepting activity and, surprisingly, in the appearance of methionine-accepting activity. Thus, both the codon and amino-acid specificity of this tRNA are converted by a single post-transcriptional modification of the first position of the anticodon during tRNA maturation.

Role of the ENTH domain in phosphatidylinositol-4,5-bisphosphate binding and endocytosis

Endocytic proteins such as epsin, AP180, and Hip1R (Sla2p) share a conserved modular region termed the epsin NH2-terminal homology (ENTH) domain, which plays a crucial role in clathrin-mediated endocytosis through an unknown target. Here, we demonstrate a strong affinity of the ENTH domain for phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2]. With nuclear magnetic resonance analysis of the epsin ENTH domain, we determined that a cleft formed with positively charged residues contributed to phosphoinositide binding. Overexpression of a mutant, epsin Lys76 --> Ala76, with an ENTH domain defective in phosphoinositide binding, blocked epidermal growth factor internalization in COS-7 cells. Thus, interaction between the ENTH domain and PtdIns(4,5)P2 is essential for endocytosis mediated by clathrin-coated pits.

Cell-free production and stable-isotope labeling of milligram quantities of proteins

We have improved the productivity of an Escherichia coli cell-free protein synthesis system. First, creatine phosphate and creatine kinase were used as the energy source regeneration system, and the other components of the reaction mixture were optimized. Second, the E. coli S30 cell extract was condensed by dialysis against a polyethylene glycol solution to increase the rate of synthesis. Third, during the protein synthesis, the reaction mixture was dialyzed against a low-molecular-weight substrate solution to prolong the reaction. Thus, the yield of chloramphenicol acetyltransferase was raised to 6 mg/ml of reaction mixture. Stable-isotope labeling of a protein with 13C/15N-labeled amino acids for NMR spectroscopy was achieved by this method.

An operational RNA code for amino acids and possible relationship to genetic code

RNA helical oligonucleotides that recapitulate the acceptor stems of transfer RNAs, and that are devoid of the anticodon trinucleotides of the genetic code, are aminoacylated by aminoacyl tRNA synthetases. The specificity of aminoacylation is sequence dependent, and both specificity and efficiency are generally determined by only a few nucleotides proximal to the amino acid attachment site. This sequence/structure-dependent aminoacylation of RNA oligonucleotides constitutes an operational RNA code for amino acids. To a rough approximation, members of the two different classes of tRNA synthetases are, like tRNAs, organized into two major domains. The class-defining conserved domain containing the active site incorporates determinants for recognition of RNA mini-helix substrates. This domain may reflect the primordial synthetase, which was needed for expression of the operational RNA code. The second synthetase domain, which generally is less or not conserved, provides for interactions with the second domain of tRNA, which incorporates the anticodon. The emergence of the genetic from the operational RNA code could occur when the second domain of synthetases was added with the anticodon-containing domain of tRNAs.

Structural basis for recognition of the tra mRNA precursor by the Sex-lethal protein

The Sex-lethal (Sxl) protein of Drosophila melanogaster regulates alternative splicing of the transformer (tra) messenger RNA precursor by binding to the tra polypyrimidine tract during the sex-determination process. The crystal structure has now been determined at 2.6 A resolution of the complex formed between two tandemly arranged RNA-binding domains of the Sxl protein and a 12-nucleotide, single-stranded RNA derived from the tra polypyrimidine tract. The two RNA-binding domains have their beta-sheet platforms facing each other to form a V-shaped cleft. The RNA is characteristically extended and bound in this cleft, where the UGUUUUUUU sequence is specifically recognized by the protein. This structure offers the first insight, to our knowledge, into how a protein binds specifically to a cognate RNA without any intramolecular base-pairing.

Structural genomics projects in Japan

Two major structural genomics projects exist in Japan. The oldest, the RIKEN Structural Genomics Initiative, has two major goals: to determine bacterial, mammalian, and plant protein structures by X-ray crystallography and NMR spectroscopy and to perform functional analyses with the target proteins. The newest, the structural genomics project at the Biological Information Research Center, focuses on human membrane proteins.

Sodium channel alpha-subunit mRNAs I, II, III, NaG, Na6 and hNE (PN1): different expression patterns in developing rat nervous system

The expression of sodium channel alpha-subunit mRNAs I, II, III, NaG, Na6 and hNE (PN1) was examined in developing (E17-P30) hippocampus, cerebellum, spinal cord and dorsal root ganglia using non-isotopic in situ hybridization cytochemistry. The results showed distinct patterns of expression for each of the sodium channel mRNAs with maturation of the nervous system. In the hippocampus, sodium channel mRNA I was not detected at any developmental time, while mRNA II showed increasing hybridization signal between E17 and P30. Sodium channel mRNA III was more prevalent at late embryonic and early postnatal times, and was barely detectable at P30. The transcript for NaG showed transient expression between P2 and P15, being expressed at low levels at E17 and not being detectable at P30. Sodium channel mRNA Na6 exhibited a high level of expression between E17 and P15 in the hippocampal formation, with an attenuation of the signal by P30. hNE (PN1) mRNA was not detected in the hippocampus at any time examined. In the cerebellum, sodium channel mRNA I was not detected at E17 or P2, but became detectable in Purkinje cells at P15 and continued to show a low level of expression in these cells at P30. mRNA I was not detected at any time examined in granule cells of the cerebellum. Sodium channel mRNA II exhibited increasing expression in the developing cerebellum, and showed increasing signal in Purkinge cells beginning on P2 and granule cells on P15. Sodium channel mRNA III was down-regulated with development in the cerebellum, although mRNA III was readily detected at E17, it was not detected in any layers of the cerebellum by P15. NaG mRNA showed a peak of expression at P2, and was present at low levels at E17 and P15 and not detectable at P30. Na6 mRNA was highly expressed in the E17 cerebellum; this mRNA was present at high levels in Purkinje cells throughout development, although in granule cells the signal was attenuated at P15-P30. Sodium channel hNE (PN1) mRNA was not detected in the cerebellum at any time in development. In the spinal cord, sodium channel mRNA I showed increasing expression beginning at P2 and was highly expressed, particularly in ventral motor neurons, by P30. Sodium channel II mRNA was detected at all stages of development in the spinal cord; in contrast, mRNA III was detected at E17 and P2, but showed very low levels of expression by P30. NaG mRNA exhibited a transient expression in spinal cord at P2, but was not detectable at E17 and P30. Na6 mRNA was detectable at very low levels at E17 and became highly expressed at P2, prior to a reduction of the signal at P15 and P30. hNE (PN1) mRNA was not detected in the spinal cord at any time in development. In the dorsal root ganglia, sodium channel I mRNA hybridization signal was detected in DRG neurons at P2, with slightly increased levels at P15 and P30. Sodium channel II mRNA exhibited a relatively constant, moderate level of expression at all developmental ages. Sodium channel III mRNA was highly expressed in DRG neurons at E17 but was down-regulated with further development so that it was not detectable by P30. NaG mRNA was strongly expressed by some DRG neurons at all stages of development from E17 to P30; in general the level of NaG labelling was greater in larger neurons than in smaller neurons. Na6 mRNA showed increasing expression with development in DRG neurons; at E17, low levels of Na6 mRNA were detected and by P15 to P30 high levels of expression were present in some neurons. hNE (PN1) mRNA was present in DRG neurons at P2, and was up-regulated with further development so that by P30 hNE (PN1) was expressed in all DRG neurons sizes. These results demonstrate that sodium channel alpha-subunit mRNAs I, II, III, NaG, Na6 and hNE (PN1) exhibit distinct spatial and temporal patterns of expression in nervous tissue, and suggest that the expression of the sodium channel alpha-subunits is differentially regulated. (ABSTRACT TRUNCATED)

Enzyme structure with two catalytic sites for double-sieve selection of substrate

High-fidelity transfers of genetic information in the central dogma can be achieved by a reaction called editing. The crystal structure of an enzyme with editing activity in translation is presented here at 2.5 angstroms resolution. The enzyme, isoleucyl-transfer RNA synthetase, activates not only the cognate substrate L-isoleucine but also the minimally distinct L-valine in the first, aminoacylation step. Then, in a second, "editing" step, the synthetase itself rapidly hydrolyzes only the valylated products. For this two-step substrate selection, a "double-sieve" mechanism has already been proposed. The present crystal structures of the synthetase in complexes with L-isoleucine and L-valine demonstrate that the first sieve is on the aminoacylation domain containing the Rossmann fold, whereas the second, editing sieve exists on a globular beta-barrel domain that protrudes from the aminoacylation domain.

Molecular mechanism of codon recognition by tRNA species with modified uridine in the first position of the anticodon

Proton NMR analyses have been made to elucidate the conformational characteristics of modified nucleotides as found in the first position of the anticodon of tRNA [derivatives of 5-methyl-2-thiouridine 5'-monophosphate (pxm5s2U) and derivatives of 5-hydroxyuridine 5'-monophosphate (pxo5U)]. In pxm5s2U, the C3'-endo form is extraordinarily more stable than the C2'-endo form for the ribose ring, because of the combined effects of the 2-thiocarbonyl group and the 5-substituent. By contrast, in pxo5U, the C2'-endo form is much more stable than the C3'-endo form, because of the interaction between the 5-substituent and the 5'-phosphate group. The enthalpy differences between the C2'-endo form and the C3'-endo form have been obtained as 1.1, -0.7, and 0.1 kcal/mol (1 cal = 4.184 J) for pxm5s2U, pxo5U, and unmodified uridine 5'-monophosphate, respectively. These findings lead to the conclusion that xm5s2U in the first position of the anticodon exclusively takes the C3'-endo form to recognize adenosine (but not uridine) as the third letter of the codon, whereas xo5U takes the C2'-endo form as well as the C3'-endo form to recognize adenosine, guanosine, and uridine as the third letter of the codon on ribosome. Accordingly, the biological significance of such modifications of uridine to xm5s2U/xo5U is in the regulation of the conformational rigidity/flexibility in the first position of the anticodon so as to guarantee the correct and efficient translation of codons in protein biosynthesis.

Tomosyn: a syntaxin-1-binding protein that forms a novel complex in the neurotransmitter release process

Syntaxin-1 is a component of the synaptic vesicle docking and/or membrane fusion soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) complex (7S and 20S complexes) in nerve terminals. Syntaxin-1 also forms a heterodimer with Munc18/n-Sec1/rbSec1 in a complex that is distinct from the 7S and 20S complexes. In this report, we identify a novel syntaxin-1-binding protein, tomosyn, that is capable of dissociating Munc18 from syntaxin-1 and forming a novel 10S complex with syntaxin-1, soluble N-etyhlmaleimide-sensitive factor attachment (SNAP) 25, and synaptotagmin. The 130 kDa isoform of tomosyn is specifically expressed in brain, where its distribution partly overlaps with that of syntaxin-1 in nerve terminals. High level expression of either syntaxin-1 or tomosyn results in a specific reduction in Ca2+-dependent exocytosis from PC12 cells. These results suggest that tomosyn is an important component in the neurotransmitter release process where it may stimulate SNARE complex formation.

Structural basis for double-sieve discrimination of L-valine from L-isoleucine and L-threonine by the complex of tRNA(Val) and valyl-tRNA synthetase

Valyl-tRNA synthetase (ValRS) strictly discriminates the cognate L-valine from the larger L-isoleucine and the isosteric L-threonine by the tRNA-dependent "double sieve" mechanism. In this study, we determined the 2.9 A crystal structure of a complex of Thermus thermophilus ValRS, tRNA(Val), and an analog of the Val-adenylate intermediate. The analog is bound in a pocket, where Pro(41) allows accommodation of the Val and Thr moieties but precludes the Ile moiety (the first sieve), on the aminoacylation domain. The editing domain, which hydrolyzes incorrectly synthesized Thr-tRNA(Val), is bound to the 3' adenosine of tRNA(Val). A contiguous pocket was found to accommodate the Thr moiety, but not the Val moiety (the second sieve). Furthermore, another Thr binding pocket for Thr-adenylate hydrolysis was suggested on the editing domain.

Effects of probucol on xanthomata regression in familial hypercholesterolemia

Fifty-one patients with familial hypercholesterolemia were treated for 2 to 4 years with probucol, cholestyramine, clofibrate and compactin in various combinations. Mean baseline serum cholesterol was 359 +/- 10 mg/dl in the heterozygote, and 582 +/- 52 mg/dl in the homozygote patients. We found that a combination of probucol, cholestyramine and compactin decreased serum cholesterol to normal or near normal in most of the heterozygote patients. In 3 severely affected heterozygote and all 8 homozygote patients, adequate cholesterol reduction was only possible with plasmapheresis plus a hypolipidemic agent. Measurement of the Achilles tendon after 12 to 16 months of treatment showed that reductions in thickness occurred in all patients taking probucol, even in a single-drug regimen, in those undergoing plasmapheresis, especially if probucol was used and in those receiving a combination of cholestyramine and compactin. Probucol was most effective in patients who experienced the greatest decreases in high density lipoprotein (HDL) levels, whereas the cholestyramine-compactin combination worked without decreasing HDL concentrations. Combined clofibrate-cholestyramine therapy, by contrast, led to increased tendon thickness in all but 1 patient. It is believed that probucol exerts its positive effect on xanthomata regression by reducing the size of HDL particles, as was shown in this study. It has already been reported that smaller HDL particles are more active in reverse cholesterol transport. The direct peripheral action of probucol may have aided regression as well.

Selective removal of low density lipoprotein by plasmapheresis in familial hypercholesterolemia

Plasma lipoproteins were selectively removed from familial hypercholesterolemic patients by using two types of plasmapheresis: double-membrane filtration and selective adsorption of very low density lipoproteins (VLDL) and low density lipoproteins (LDL). In both techniques, plasma was separated from blood cells by using hollow-fiber filters, and 100% of the VLDL and LDL was recovered in the filtrate. In double-membrane filtration, the second hollow-fiber filter trapped 84% of LDL + VLDL, 48% of high density lipoprotein (HDL), 24% of albumin, and 46% of the remaining plasma protein. By treating 3 liters of plasma from a patient weighing 60 kg, 60% of the LDL and 30% to 40% of the HDL were removed as a result of an exponential decay of each component with the respective trapping coefficients. When dextran sulfate-cellulose was used as a LDL sorbent, there was only loss of LDL and VLDL, and no loss of any other major plasma component or of HDL. The sorbent column (400 ml) was saturated with 7.5 g of LDL cholesterol by treatment with 3.5 liters of plasma; the maximum reduction of LDL cholesterol was thus about 300 mg/dl for the patient weighing 60 kg. No serious side effects were observed during the long-term trials (19 to 27 months for four patients on double-membrane filtration and 10 months for the two patients on dextran sulfate-cellulose treatment.

Oncogenic Ras triggers cell suicide through the activation of a caspase-independent cell death program in human cancer cells

To prevent neoplasia, cells of multicellular organisms activate cellular disposal programs such as apoptosis in response to deregulated oncogene expression, making the suppression of such programs an essential step for potentially neoplastic cells to become established as clinically relevant tumors. Since the mutation of ras proto-oncogenes, the most frequently mutated proto-oncogenes in human tumors, is very rare in some tumor types such as glioblastomas and gastric cancers, we hypothesized that mutated ras genes might activate a cell death program that cannot be overcome by these tumor types. Here we show that the expression of oncogenically mutated ras gene induces cellular degeneration accompanied by cytoplasmic vacuoles in human glioma and gastric cancer cell lines. Cells dying as a result of oncogenic Ras expression had relatively well-preserved nuclei that were negative for TUNEL staining. An immunocytochemical analysis demonstrated that the cytoplasmic vacuoles are derived mainly from lysosomes. This oncogenic Ras-induced cell death occurred in the absence of caspase activation, and was not inhibited by the overexpression of anti-apoptotic Bcl-2 protein. These observations suggested that oncogenic Ras-induced cell death is most consistent with a type of programmed cell death designated 'type 2 physiological cell death' or 'autophagic degeneration', and that this cell death is regulated by a molecular mechanism distinct from that of apoptosis. Our findings suggest a possible role for this non-apoptotic cell death in the prevention of neoplasia, and the activation of the non-apoptotic cell death program may become a potential cancer therapy complementing apoptosis-based therapies. In addition, the approach used in this study may be a valuable way to find genetically-regulated cell suicide programs that cannot be overcome by particular tumor types.

A highly efficient cell-free protein synthesis system from Escherichia coli

We modified a cell-free coupled transcription/translation system from Escherichia coli with the T7 phage RNA polymerase, and achieved a productivity as high as 0.4 mg protein/ml reaction mixture. First, we found that the optimal concentrations of phosphoenolpyruvate and poly(ethylene glycol) are interdependent; higher concentrations of the former should be used at higher concentrations of the latter. Second, the use of a condensed 30000 x g cell extract, in place of the conventional one, significantly increased the initial rate of protein synthesis. This phenomenon was demonstrated to be due to a reason other than elimination of inhibitory molecule(s) from the extract. For this system with the condensed extract, the phosphoenolpyruvate and poly(ethylene glycol) concentrations were again co-optimized, resulting in production of chloramphenicol acetyltransferase at a productivity of 0.3 mg/ml. Finally, the productivity was further increased up to 0.4 mg/ml, by supplementation of the pool of amino acids. This improved cell-free protein synthesis system is superior in productivity to any other cell-free systems reported so far, including the continuous-flow cell-free system.

Conformational rigidity of specific pyrimidine residues in tRNA arises from posttranscriptional modifications that enhance steric interaction between the base and the 2'-hydroxyl group

In order to elucidate roles of the 2'-O-methylation of pyrimidine nucleotide residues of tRNAs, conformations of 2'-O-methyluridylyl(3'----5')uridine (UmpU), 2'-O-methyluridine 3'-monophosphate (Ump), and 2'-O-methyluridine (Um) in 2H2O solution were analyzed by one- and two-dimensional proton NMR spectroscopy and compared with those of related nucleotides and nucleoside. As for UpU and UmpU, the 2'-O-methylation was found to stabilize the C3'-endo form of the 3'-nucleotidyl unit (Up-/Ump-moiety). This stabilization of the C3'-endo form is primarily due to an intraresidue effect, since the conformation of the 5'-nucleotidyl unit (-pU moiety) was only slightly affected by the 2'-O-methylation of the 3'-nucleotide unit. In fact even for Up and Ump, the 2'-O-methylation significantly stabilizes the C3'-endo form by 0.8 kcal/.mol-1. By contrast, for nucleosides (U and Um), the C3'-endo form is slightly stabilized by 0.1 kcal/.mol-1. Accordingly, the stabilization of the C3'-endo form by the 2'-O-methylation is primarily due to the steric repulsion among the 2-carbonyl group, the 2'-O-methyl group and the 3'-phosphate group in the C2'-endo form. For some tRNA species, 2-thiolation of pyrimidine residues is found in positions where the 2'-O-methylation is found for other tRNA species.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effects of cholesterol lowering and angiotensin-converting enzyme inhibition on coronary atherosclerosis: The Simvastatin/Enalapril Coronary Atherosclerosis Trial (SCAT)

BACKGROUND

This long-term, multicenter, randomized, double-blind, placebo-controlled, 2 x 2 factorial, angiographic trial evaluated the effects of cholesterol lowering and angiotensin-converting enzyme inhibition on coronary atherosclerosis in normocholesterolemic patients.

METHODS AND RESULTS

There were a total of 460 patients: 230 received simvastatin and 230, a simvastatin placebo, and 229 received enalapril and 231, an enalapril placebo (some subjects received both drugs and some received a double placebo). Mean baseline measurements were as follows: cholesterol level, 5.20 mmol/L; triglyceride level, 1.82 mmol/L; HDL, 0.99 mmol/L; and LDL, 3.36 mmol/L. Average follow-up was 47.8 months. Changes in quantitative coronary angiographic measures between simvastatin and placebo, respectively, were as follows: mean diameters, -0.07 versus -0.14 mm (P:=0.004); minimum diameters, -0.09 versus -0.16 mm (P:=0. 0001); and percent diameter stenosis, 1.67% versus 3.83% (P:=0.0003). These benefits were not observed in patients on enalapril when compared with placebo. No additional benefits were seen in the group receiving both drugs. Simvastatin patients had less need for percutaneous transluminal coronary angioplasty (8 versus 21 events; P:=0.020), and fewer enalapril patients experienced the combined end point of death/myocardial infarction/stroke (16 versus 30; P:=0.043) than their respective placebo patients.

CONCLUSIONS

This trial extends the observation of the beneficial angiographic effects of lipid-lowering therapy to normocholesterolemic patients. The implications of the neutral angiographic effects of angiotensin-converting enzyme inhibition are uncertain, but they deserve further investigation in light of the positive clinical benefits suggested here and seen elsewhere.

Potassium channels from NG108-15 neuroblastoma-glioma hybrid cells. Primary structure and functional expression from cDNAs

The complete amino acid sequences of two potassium channel proteins from NG108-15 neuroblastoma-glioma hybrid cells have been deduced by cloning and sequencing the cDNAs. One of these proteins (NGK2) is structurally more closely related to the Drosophila Shaw gene product than to the Shaker and Shab gene products, whereas the other (NGK1) is identical with a rat brain potassium channel protein (BK2) which is more closely related to the Drosophila Shaker gene product. mRNAs derived from both the cloned cDNAs, when injected into Xenopus oocytes, direct the formation of functional potassium channels with properties of delayed rectifiers.

Structural basis for the recognition of isoleucyl-adenylate and an antibiotic, mupirocin, by isoleucyl-tRNA synthetase

An analogue of isoleucyl-adenylate (Ile-AMS) potently inhibits the isoleucyl-tRNA synthetases (IleRSs) from the three primary kingdoms, whereas the antibiotic mupirocin inhibits only the eubacterial and archaeal IleRSs, but not the eukaryotic enzymes, and therefore is clinically used against methicillin-resistant Staphylococcus aureus. We determined the crystal structures of the IleRS from the thermophilic eubacterium, Thermus thermophilus, in complexes with Ile-AMS and mupirocin at 3.0- and 2.5-A resolutions, respectively. A structural comparison of the IleRS.Ile-AMS complex with the adenylate complexes of other aminoacyl-tRNA synthetases revealed the common recognition mode of aminoacyl-adenylate by the class I aminoacyl-tRNA synthetases. The Ile-AMS and mupirocin, which have significantly different chemical structures, are recognized by many of the same amino acid residues of the IleRS, suggesting that the antibiotic inhibits the enzymatic activity by blocking the binding site of the high energy intermediate, Ile-AMP. In contrast, the two amino acid residues that concomitantly recognize Ile-AMS and mupirocin are different between the eubacterial/archaeal IleRSs and the eukaryotic IleRSs. Mutagenic analyses revealed that the replacement of the two residues significantly changed the sensitivity to mupirocin.

Coendocytosis of cadherin and c-Met coupled to disruption of cell-cell adhesion in MDCK cells--regulation by Rho, Rac and Rab small G proteins

Both E-cadherin, a cell-cell adhesion molecule, and c-Met, the hepatocyte growth factor (HGF)/scatter factor (SF) receptor, were colocalized at cell-cell adhesion sites of MDCK cells. HGF/SF or a phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), induced disruption of cell-cell adhesion, which was accompanied by endocytosis of both E-cadherin and c-Met. Reduction of medium Ca2+ to a micromolar range showed the same effects. Re-increase in medium Ca2+ to a millimolar range formed cell-cell adhesion, which was accompanied by exocytosis of E-cadherin and c-Met, followed by their re-colocalization at the cell-cell adhesion sites. These results suggest that E-cadherin and c-Met are colocalized at cell-cell adhesion sites and undergo co-endo-exocytosis. We have previously shown that TPA does not induce disruption of cell-cell adhesion and subsequent scattering of MDCK cells stably expressing a dominant active mutant of RhoA or Rac1 small G protein or a dominant negative mutant of Rab5 small G protein. In these cell lines, the HGF- or TPA-induced coendocytosis of E-cadherin and c-Met was inhibited, but the coendocytosis of E-cadherin and c-Met in response to reduction of medium Ca2+ was not affected. Wortmannin, an inhibitor of phosphoinositide (PI) 3-kinase, inhibited the HGF-induced disruption of cell-cell junction and endocytosis of E-cadherin and c-Met, but not the TPA-induced ones. These results suggest that disruption of cell-cell adhesion is involved in the HGF- or TPA-induced coendocytosis of E-cadherin and c-Met in MDCK cells, and that the Rho and Rab family members indirectly regulate this coendocytosis. In addition, coendocytosis of E-cadherin and c-Met in response to HGF is partly mediated by PI 3-kinase. The cross-talk between cell-cell and cell-matrix adherens junctions is discussed.

The molecular genetics and evolution of red and green color vision in vertebrates

To better understand the evolution of red-green color vision in vertebrates, we inferred the amino acid sequences of the ancestral pigments of 11 selected visual pigments: the LWS pigments of cave fish (Astyanax fasciatus), frog (Xenopus laevis), chicken (Gallus gallus), chameleon (Anolis carolinensis), goat (Capra hircus), and human (Homo sapiens);and the MWS pigments of cave fish, gecko (Gekko gekko), mouse (Mus musculus), squirrel (Sciurus carolinensis), and human. We constructed these ancestral pigments by introducing the necessary mutations into contemporary pigments and evaluated their absorption spectra using an in vitro assay. The results show that the common ancestor of vertebrates and most other ancestors had LWS pigments. Multiple regression analyses of ancestral and contemporary MWS and LWS pigments show that single mutations S180A, H197Y, Y277F, T285A, A308S, and double mutations S180A/H197Y shift the lambda(max) of the pigments by -7, -28, -8, -15, -27, and 11 nm, respectively. It is most likely that this "five-sites" rule is the molecular basis of spectral tuning in the MWS and LWS pigments during vertebrate evolution.