Novel semi-synthetic glycopeptide antibiotics active against methicillin-resistant staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE): doubly-modified water-soluble derivatives of chloroorienticin B

A series of N-alkylated and aminomethylated derivatives of chloroorienticin B, a vancomycin-related glycopeptide antibiotic, were synthesized. Doubly-modified derivatives having both hydrophobic and hydrophilic substituents exhibited potent antibacterial activity against MRSA and VRE along with considerable water-solubility.     

Functional Diversity of Xyloglucan-Related Proteins and its Implications in the Cell Wall Dynamics in Plants

Abstract: The plant cell wall is a dynamic apparatus responsible for both morphogenesis and responsiveness to environmental conditions. In the cell wall of most seed plants, cellulose microfibrils are cross-linked by xyloglucans to form a cellulose/xyloglucan framework, which functions as the mechanical underpinning of the cell wall. Endoxyloglucan transferases are a class of enzymes that play a central role in construction and modification of the plant cell wall. These enzymes are encoded by a large multi-gene family termed xyloglucan-related proteins (XRPs). More than 24 members of the XRP family have so far been identified in Arabidopsis thaliana. Each member of this family functions as either a hydrolase or a transferase acting on xyloglucans. The primary structures of proteins and gene-expression profiles have strongly suggested their potentially divergent roles in plant morphogenesis: different members of this family are expressed in different types of tissues at distinct developmental stages and respond differentially to individual hormones as well as environmental stimuli. These facts imply that each member of this gene family is individually committed to a specific process that proceeds in a specific tissue at a specific stage of development. Probably the generation and maintenance of the cell walls in a whole organ, and thus in the whole plant, is achieved by the ensemble of individual members of the XRP family.     

Effects of hypergravity on growth and cell wall properties of cress hypocotyls

Elongation growth of etiolated hypocotyls of cress (Lepidium sativum L.) was suppressed when they were exposed to basipetal hypergravity at 35 x g and above. Acceleration at 135 x g caused a decrease in the mechanical extensibility and an increase in the minimum stress-relaxation time of the cell wall. Such changes in the mechanical properties of the cell wall were prominent in the lower regions of hypocotyls. The amounts of cell wall polysaccharides per unit length of hypocotyls increased under the hypergravity condition and, in particular, the increase in the amount of cellulose in the lower regions was conspicuous. Hypergravity did not influence the neutral sugar composition of either the pectin or the hemicellulose fraction. The amount of lignin was also increased by hypergravity treatment, although the level was low. The data suggest that hypergravity modifies the metabolism of cell wall components and thus makes the cell wall thick and rigid, thereby inhibiting elongation growth of cress hypocotyls. These changes may contribute to the plants' ability to sustain their structures against hypergravity.     

Endo-xyloglucan transferase,a new class of transferase involved in cell wall construction

Cell shape in plants is constrained by cell walls, which are thick yet dynamic structures composed of crystalline cellulose microfibrils and matrix polymers. Xyloglucans are the principal component of the matrix polymers and bind tightly to the surface of cellulose microfibrils and thereby cross-link them to form an interwoven xyloglucan-cellulose network structure. Thus, cleavage and reconnection of the cross-links between xyloglucan molecules are required for the rearrangement of the cell wall architecture, the process essential for both cell wall expansion and the wall deposition occurring during cell growth and differentiation. Endoxyloglucan transferase (EXT) is a newly identified class of transferase that catalyzes molecular grafting between xyloglucan molecules. This enzyme catalyzes both endo-type splitting of a xyloglucan molecule and reconnection of a newly generated reducing terminus of the xyloglucan to the non-reducing terminus of another xyloglucan molecule, thereby mediating molecular grafting between xyloglucan cross-links in plant cell walls. Molecular cloning and sequencing of EXT-cDNAs derived from five different plant species includingA. thaliana andV. angularis has revealed that the amino acid sequence of the mature protein is extensively conserved in the five different plant species, indicating that EXT protein is ubiquitous among higher plants. This structural study has also disclosed the presence of a group of xyloglucan related proteins (XRPs) with transferase activity in higher plants. Current data strongly suggest that these proteins are involved in a wide spectrum of physiological activities including cell wall expansion and deposition in growing cell walls. Recipient of the Botanical Sociaty Award of Young Scientists, 1993.     

Enzymic Analysis of Feruloylated Arabinoxylans (Feraxan) Derived from Zea mays Cell Walls : II. Fractionation and Partial Characterization of Feraxan Fragments Dissociated by a Bacillus subtilis Enzyme (Feraxanase)

Structural features of feruloylated arabinoxylan (feraxan) present in Zea mays L. (hybrid B 73 × Mo 17) coleoptile cell walls have been studied using a purified feraxan-dissociating enzyme (feraxanase) and an α-arabinofuranosidase. This experimental approach has demonstrated the following. (a) Feraxanase dissociated ca. 20% (dry weight basis) of the maize wall preparation. The predominant oligosaccharides enzymically liberated were allocated into seven major subfractions designated A-1 (0.8%), B-1 (1.6%), B-2 (2.4%), B-3 (4.6%), C-1 (1.0%), C-2 (4.2%), and C-3 (0.3%). Values in parentheses reflect the percentage of the wall associated with each subfraction. Subfractions represent samples enriched in different degrees of polymerization, sugar composition, linkage arrangements, and phenolic acid content. (b) B-1, B-2, and B-3 fractions are not feruloylated and have smaller molecular mass (less than 10⁴ kilodaltons) and consist chiefly of t-arabinosyl-5-arabinosyl, 4-xylosyl, 2,4/3,4-xylosyl, and glucuronosyl residues, suggesting that these fragments constitute nonferuloylated regions of arabinoxylan. (c) C-2 and C-3 fractions contain ferulic acid (6.2% and 12.1%, respectively) and are similar to the B series in their sugar linkage arrangements but were derived from feruloylated regions. (d) Alkali treatment of the C-2 fraction decreases the molecular size of the fragment and liberates phenolic acids. The results suggest the presence of alkaline-labile links, probably diferulate bridges. (e) A-1 and C-1 fractions are larger (more than 5 × 10⁵ kilodalton) and contain t-galactosyl-, 4-galactosyl, 2,4-rhamnosyl-residues, galacturonic acid, and the sugar linkage arrangements common to other fractions. The A-1 fraction is not feruloylated, whereas C-1 fraction contains 0.5% ferulic acid. The presence of galactose, rhamnose, and galacturonic acid suggests that pectic polymers, probably homopolygalacturonans and rhamnogalacturonans, are linked to nonferuloylated and feruloylated segments of arabinoxylans.     

Premature chromosome condensation is induced by a point mutation in the hamster RCC1 gene.

At the nonpermissive temperature, premature chromosome condensation (PCC) occurs in tsBN2 cells derived from the BHK cell line, which can be converted to the Ts+ phenotype by the human RCC1 gene. To prove that the RCC1 gene is the mutant gene in tsBN2 cells, which have RCC1 mRNA and protein of the same sizes as those of BHK cells, RCC1 cDNAs were isolated from BHK and tsBN2 cells and sequenced to search for mutations. The hamster (BHK) RCC1 cDNA encodes a protein of 421 amino acids homologous to the human RCC1 protein. In a comparison of the base sequences of BHK and BN2 RCC1 cDNAs, a single base change, cytosine to thymine (serine to phenylalanine), was found in the 256th codon of BN2 RCC1 cDNA. The same transition was verified in the RCC1 genomic DNA by the polymerase chain reaction method. BHK RCC1 cDNA, but not tsBN2 RCC1 cDNA, complemented the tsBN2 mutation, although both have the same amino acid sequence except for one amino acid at the 256th codon. This amino acid change, serine to phenylalanine, was estimated to cause a profound structural change in the RCC1 protein.     

Modifications of cell wall polysaccharides during auxin-induced growth in azuki bean epicotyl segments

Changes in sugar compositions and the distribution pattern ofthe molecular weight of cell wall polysaccharides during indole-3-aceticacid (IAA)-induced cell elongation were investigated. Differentialextraction of the cell wall and gel permeation chroma-tographyof wall polysaccharides indicated that galactans, polyuronides,xylans, glucans and cellulose were present in the azuki beanepicotyl cell wall. When segments were incubated in the absence of sucrose, IAAenhanced the degradation of galactans in both the pectin andhemicellulose fractions, whereas to some extent it enhancedthe polymerization of xylans and glucans in the hemicellulosefraction and an increase in the amounts of polyuronides in thepectin fraction and of -cellulose. In the presence of 50 mMsucrose, IAA caused large increases in the amounts of all thewall polysaccharides, and enhanced the polymerization of galactans,xylans and glucans in the hemicellulose fraction. These results and an important role of galactan turnover incell wall extension are discussed. (Received December 11, 1979; )     

Loss of RCC1, a nuclear DNA-binding protein, uncouples the completion of DNA replication from the activation of cdc2 protein kinase and mitosis.

The temperature-sensitive mutant cell line tsBN2, was derived from the BHK21 cell line and has a point mutation in the RCC1 gene. In tsBN2 cells, the RCC1 protein disappeared after a shift to the non-permissive temperature at any time in the cell cycle. From S phase onwards, once RCC1 function was lost at the non-permissive temperature, p34cdc2 was dephosphorylated and M-phase specific histone H1 kinase was activated. However, in G1 phase, shifting to the non-permissive temperature did not activate p34cdc2 histone H1 kinase. The activation of p34cdc2 histone H1 kinase required protein synthesis in addition to the presence of a complex between p34cdc2 and cyclin B. Upon the loss of RCC1 in S phase of tsBN2 cells and the consequent p34cdc2 histone H1 kinase activation, a normal mitotic cycle is induced, including the formation of a mitotic spindle and subsequent reformation of the interphase-microtubule network. Exit from mitosis was accompanied by the disappearance of cyclin B, and a decrease in p34cdc2 histone H1 kinase activity. The kinetics of p34cdc2 histone H1 kinase activation correlated well with the appearance of premature mitotic cells and was not affected by the presence of a DNA synthesis inhibitor. Thus the normal inhibition of p34cdc2 activation by incompletely replicated DNA is abrogated by the loss of RCC1.