Glucosinolates, a natural chemical arsenal: More to tell than the myrosinase story.

Glucosinolates are a group of thioglucosides that belong to the class of plant nitrogen-containing natural products. So far, very little biological activity has been associated with intact glucosinolates. The hydrolysis of glucosinolates has, for long, attracted attention because of the potent biological activity of the hydrolysis products. From allelopathic to antiparasitic, antimicrobial and antineoplastic effects, the activity spectrum of the degradation products of typical glucosinolates has been the subject of much research. The present review seeks to address the various means of glucosinolate degradation (thermal, enzymatic, or chemical degradation) and the ensuing products. It also aims to draw a comparative profile of the various antimicrobial effects of these degradation products to provide a further understanding of the biological function of these important compounds.

UbK is Involved in the Resistance of Bacillus Subtilis to Oxidative Stress.

The objective of this study was to assess the role of UbK, a novel protein kinase, in the growth of Bacillus subtilis, especially under oxidative stress conditions. Growth profiles of wild-type and ΔubK mutant strains were assessed in the presence of paraquat, an in vivo inducer of oxidative stress. Wild-type B. subtilis cells were able to efficiently survive the stress conditions, whereas the growth profile of the ΔubK mutant strain was significantly affected. Complementation of the ΔubK mutant with a plasmid coding for a wild-type UbK restored wild-type growth phenotypes. Furthermore, we used recombinant plasmids containing the genes of the active kinase (UbK) and its inactive form (E106AUbK) to transform wild-type and ΔubK mutant strains. Our results showed that an active form of UbK is needed to restore a normal growth profile. Protein kinases allow a fine-tuning of cellular processes, including those related to metabolic adaptation to environmental cues. Our findings highlight the importance of an active UbK in the bacterial growth under oxidative stress in B. subtilis. This study revealed the role of a new protein kinase, UbK, allowing B. subtilis to survive oxidative stress.

Expanding the Kinome World: A New Protein Kinase Family Widely Conserved in Bacteria.

Fine tuning of signaling pathways is essential for cells to cope with sudden environmental variations. This delicate balance is maintained in particular by protein kinases that control the activity of target proteins by reversible phosphorylation. In addition to homologous eukaryotic enzymes, bacteria have evolved some specific Ser/Thr/Tyr protein kinases without any structural resemblance to their eukaryotic counterparts. Here, we show that a previously identified family of ATPases, broadly conserved among bacteria, is in fact a new family of protein kinases with a Ser/Thr/Tyr kinase activity. A prototypic member of this family, YdiB from Bacillus subtilis, is able to autophosphorylate and to phosphorylate a surrogate substrate, the myelin basic protein. Two crystal structures of YdiB were solved (1.8 and 2.0Å) that display a unique ATP-binding fold unrelated to known protein kinases, although a conserved HxD motif is reminiscent of that found in Hanks-type protein kinases. The effect of mutations of conserved residues further highlights the unique nature of this new protein kinase family that we name ubiquitous bacterial kinase. We investigated the cellular role of YdiB and showed that a ∆ydiB mutant was more sensitive to paraquat treatment than the wild type, with ~13% of cells with an aberrant morphology. In addition, YdiE, which is known to participate with both YdiC and YdiB in an essential chemical modification of some specific tRNAs, is phosphorylated in vitro by YdiB. These results expand the boundaries of the bacterial kinome and support the involvement of YdiB in protein translation and resistance to oxidative stress in B. subtilis.

Water-stress-induced inhibition of α-tubulin gene expression during growth, and its implications for reproductive success in rice.

A drought-suppressed cDNA (RiP-3), encoding a putative α-tubulin protein was isolated from rice panicle at pollen-mother-cell meiosis stage. Analysis of its deduced amino acid sequence showed all the typical structural motifs for plant α-tubulins. The expression of α-tubulin transcripts was observed in all the reproductive organs of rice panicle, and in 5- or 15-day old seedlings, but not in mature leaves. Expression levels were positively correlated with the regions and periods of high growth, and the transcript level declined in parallel with drought-induced reduction in growth rates in all tissues examined. Immunoblot analysis of proteins separated by SDS-PAGE with anti-α-tubulin monoclonal antibody showed that the level of protein paralleled the changes in the transcript abundance in these organs. In situ immunolocalization of the α-tubulin protein in sections of the basal part of 5-day old seedlings showed that the highest levels of the protein were associated with the fastest growing leaf whorls, and the protein level declined upon a brief episode of water stress. Given the known critical role of tubulin in cell division and elongation, the results indicate that the expression of α-tubulin gene may be part of the events that suppress panicle elongation during water deficit, which is in turn a suspected cause of male reproductive failure and yield reduction in rice.

Cloning and functional expression of two plant thiol methyltransferases: a new class of enzymes involved in the biosynthesis of sulfur volatiles.

Glucosinolates are defensive compounds found in several plant families. We recently described five distinct isoforms of a novel plant enzyme, thiol methyltransferase (TMT), which methylate the hydrolysis products of glucosinolates to volatile sulfur compounds that have putative anti-insect and anti-pathogen roles. In the work presented here, two cDNAs encoding these enzymes (cTMT1 and cTMT2) were isolated by screening a cabbage cDNA library with an Arabidopsis EST showing high sequence homology to one TMT isoform. The genomic clone of cTMT1 was subsequently amplified by PCR. Both cDNAs encoded polypeptides of identical lengths (227 amino acids) and similar predicted masses (ca. 25 kDa), but differing in 13 residues. The cDNAs contained the typical methyltransferase signatures, but were otherwise distinct from conventionally known N-, O- or S-methyltransferases. A chloride methyl transferase was the only gene with an assigned function that shared significant similarity with the TMT cDNAs. Southern analysis indicated single copy for each TMT gene. The two cDNAs were expressed in Escherichia coli. The substrate range, kinetic properties and molecular sizes of the purified recombinant proteins were comparable to those of the native enzyme. These data, together with the detection of the sequenced amino acid motif of one native TMT peptide in the cDNAs, confirmed that the latter were authentic TMTs. The expression pattern of the TMTs in various cabbage tissues was consistent with their association with glucosinolates. The cloning of this new class of plant genes furnishes crucial molecular tools to understand the role of this metabolic sector in plant defenses against biotic stress.