Spontaneous asparaginyl deamidation of canine milk lysozyme under mild conditions

Asparaginyl deamidation is a common form of nonenzymatic degradation of proteins and peptides. As it introduces a negative charge spontaneously and irreversibly, charge heterogeneity can be accumulated in protein solution during purification, preservation, and experiments. In this study, canine milk lysozyme (CML), a useful model for the study of the molten globule state, exhibited charge heterogeneity after sample purification. Four Asn residues in CML deamidated rapidly under mild conditions: pH 8.0 and 30 degrees C. Other than these residues, one Asn residue, which was stable in the native state, was labile to deamidation in the unfolded state. This suggests that the structural formation around Asn can suppress deamidation. Substitutions of these labile Asn residues to Gln residues prevented deamidation effectively. Because the substitutions did not disrupt the structural formation of the native and molten globule states, they will enable more precise analyses for physical and structural studies.     

Control by Ammonium Ion of the Change from Step-Up to Step-Down Photophobically Responding Cells in the Flagellate Alga Euglena gracilis

The regulation between step-down and step-up photophobic responses,resulting in photoaccumulation of the cells in an actinic lighttrap or cells' avoidance from an excessive illumination, iscrucially important for the survival of phototrophic organismssuch as Euglena gracilis. As for the factors involved in thisregulation in Euglena gracilis, we for the first time reporthere that ammonium ion specifically enhances step-down photophobicresponse, together with the effects of L-methionine-DL-sulfoximine(L-MSO), an inhibitor of ammonium assimilation, to specificallyenhance step-up photophobic response. The apparent positivecorrelation between the degree of greening and the step-downphotophobic response did not seem to reflect real causal relationshipin view of the results with effects of gabaculine, an inhibitorof -aminolaevulinic acid (-ALA) formation. The transmissionof stigma and step-down appearance did not show any correlationeither, in contrast to a previous assumption by other authors.Cycloheximide (CHX), an inhibitor of eukaryotic protein synthesis,suppressed step-down appearance and enhanced step-up appearance,probably suggesting an involvement of some (newly synthesized)protein(s) specifically in the step-down photosignal detectionand/or signal transduction process(es). (Received August 18, 1998; Accepted December 3, 1998)     

Enantioseparation properties of (1-->6)-alpha-D-glucopyranan and (1-->6)-alpha-D-mannopyranan tris(phenylcarbamate)s as chiral stationary phases in HPLC

Synthetic polysaccharides, (1-->6)-alpha-D-glucopyranan (3a) and (1-->6)-alpha-D-mannopyranan (3b), were prepared by the cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-beta-D-glucopyranose (1a) and 1,6-anhydro-2,3,4-O-6-allyl-beta-D-mannopyranose (1b), followed by the cleavage of the allyl ether linkage of 2,3,4-tri-O-allyl-(1-->6)-alpha-D-glucopyranan (2a) and 2,3,4-tri-O-allyl-(1-->6)-alpha-D-mannopyranan (2b), respectively. 2,3,4-Tris-O-(3,5-dimethylphenylcarbamoyl)- and 2,3,4-tris-O-(3,5-dichlorophenylcarbamoyl)-(1-->6)-alpha-D-glucopyranan (CSP-1 and CSP-2, respectively) and 2,3,4-tris-O-(3,5-dimethylphenylcarbamoyl)- and 2,3,4-tris-O-(3,5-dichlorophenylcarbamoyl)-(1-->6)-alpha-D-mannopyranan (CSP-3 and CSP-4, respectively) were prepared by the reaction of 3 with the corresponding 3,5-disubstituted phenylisocyanates and the chiral recognition abilities of CSP-1-4 as chiral stationary phases (CSPs) in high-performance liquid chromatography (HPLC) were evaluated. Racemic compounds such as trans-cyclopropanedicarboxylic acid dianilide (9), 1,2,2,2-tetraphenylethanol (10), flavanone (11), Tr?ger's base (12), benzoin (13), and cobalt(III) tris(acetylacetonate) (14) were efficiently resolved using CSP-1-4. For comparison among CSPs, the chiral recognition properties of the (1-->6)-alpha-D-glucopyranan CSPs were different from that of the (1-->6)-alpha-D-mannopyranan CSPs, and CSP-4 exhibited the highest chiral recognition ability among the CSPs. The resolution factors of 12 and 14 were 0.42 and 0.56 for CSP-1, 0.32 and 2.16 for CSP-2, 1.80 and 0.84 for CSP-3, and 2.31 and 8.26 for CSP-4, respectively.     

Structural principles of leucine-rich repeat (LRR) proteins

LRR-containing proteins are present in over 2000 proteins from viruses to eukaryotes. Most LRRs are 20-30 amino acids long, and the repeat number ranges from 2 to 42. The known structures of 14 LRR proteins, each containing 4-17 repeats, have revealed that the LRR domains fold into a horseshoe (or arc) shape with a parallel beta-sheet on the concave face and with various secondary structures, including alpha-helix, 3(10)-helix, and pII helix on the convex face. We developed simple methods to charactere quantitatively the arc shape of LRR and then applied them to all known LRR proteins. A quantity of 2Rsin(phi/2), in which R and phi are the radii of the LRR arc and the rotation angle about the central axis per repeating unit, respectively, is highly conserved in all the LRR proteins regardless of a large variety of repeat number and the radius of the LRR arc. The radii of the LRR arc with beta-alpha structural units are smaller than those with beta-3(10) or beta-pII units. The concave face of the LRR beta-sheet forms a surface analogous to a part of a M?bius strip.     

Unique reactivity of alpha,beta-unsaturated carboxylic acid imidazolides: catalytic asymmetric synthesis of alpha,beta-epoxy esters and alpha,beta-epoxy carboxylic acid derivatives

Catalytic asymmetric synthesis of alpha,beta-epoxy esters and alpha,beta-epoxy carboxylic acid derivatives is described. Catalytic asymmetric epoxidation of alpha,beta-unsaturated carboxylic acid imidazolides using La-BINOL-Ph(3)As=O complex gave the corresponding alpha,beta-epoxy peroxy tert-butyl esters, which were directly converted to the alpha,beta-epoxy methyl esters by adding methanol to the reaction. This catalytic system had broad generality for epoxidation of various substrates. With the use of 5-10 mol% of the catalyst, both beta-aryl and beta-alkyl-substituted-alpha,beta-epoxy methyl esters were obtained in up to 91% yield and in up to 93% enantiomeric excess. In addition, efficient transformations of alpha,beta-epoxy peroxy tert-butyl esters into the alpha,beta-epoxy amides, alpha,beta-epoxy aldehydes, and gamma,delta-epoxy beta-keto esters are also reported.     

Functional diversification of kir7.1 in cichlids accelerated by gene duplication

Mutation in the inward rectifier potassium channel gene, kir7.1, was previously identified as being responsible for the broader stripe zebrafish skin pattern mutant, jaguar/obelix. An amino acid substitution in this channel causes a broader stripe pattern than that of wild type zebrafish. In this study we analyzed cichlid homologs of the zebrafish kir7.1 gene. We identified two kinds of homologous genes in cichlids and named them cikir7.1 and cikir7.2. Southern hybridization using cichlid genome revealed that cichlids from the African Great Lakes, South America and Madagascar have two copies of the gene. Cichlids from Sri Lanka, however, showed only one band in this experiment. Database analysis revealed that only one copy of the kir7.1 gene exists in the genomes of the teleosts zebrafish, tetraodon, takifugu, medaka and stickleback. The deduced amino acid sequence of cikir7.1 is highly conserved among African cichlids, whereas that of cikir7.2 has several amino acid substitutions even in conserved transmembrane domains. Gene expression analysis revealed that cikir7.1 is expressed specifically in brain and eye, and cikir7.2 in testis and ovary; zebrafish kir7.1, however, is expressed in brain, eye, skin, caudal fin, testis and ovary. These results suggest that gene duplication of the cichlid kir7.1 occurred in a common ancestor of the family Cichlidae, that the function of parental kir7.1 was then divided into two genes, cikir7.1 and cikir7.2, and that the evolutionary rate of cikir7.2 might have been accelerated, thereby effecting functional diversification in the cichlid lineage. Thus, the evolution of kir7.1 genes in cichlids provides a typical example of gene duplication--one gene is conserved while the other becomes specialized for a novel function.     

Predictive Modeling of Drug Response in Non-Hodgkin’s Lymphoma

We combine mathematical modeling with experiments in living mice to quantify the relative roles of intrinsic cellular vs. tissue-scale physiological contributors to chemotherapy drug resistance, which are difficult to understand solely through experimentation. Experiments in cell culture and in mice with drug-sensitive (Eµ-myc/Arf-/-) and drug-resistant (Eµ-myc/p53-/-) lymphoma cell lines were conducted to calibrate and validate a mechanistic mathematical model. Inputs to inform the model include tumor drug transport characteristics, such as blood volume fraction, average geometric mean blood vessel radius, drug diffusion penetration distance, and drug response in cell culture. Model results show that the drug response in mice, represented by the fraction of dead tumor volume, can be reliably predicted from these inputs. Hence, a proof-of-principle for predictive quantification of lymphoma drug therapy was established based on both cellular and tissue-scale physiological contributions. We further demonstrate that, if the in vitro cytotoxic response of a specific cancer cell line under chemotherapy is known, the model is then able to predict the treatment efficacy in vivo. Lastly, tissue blood volume fraction was determined to be the most sensitive model parameter and a primary contributor to drug resistance.     

Fast manipulation of cellular cAMP level by light in vivo

The flagellate Euglena gracilis contains a photoactivated adenylyl cyclase (PAC), consisting of the flavoproteins PACalpha and PACbeta. Here we report functional expression of PACs in Xenopus laevis oocytes, HEK293 cells and in Drosophila melanogaster, where neuronal expression yields light-induced changes in behavior. The activity of PACs is strongly and reversibly enhanced by blue light, providing a powerful tool for light-induced manipulation of cAMP in animal cells.