No abstract

Summary• Peroxidases are involved in several important processes, such as development and responses to environmental cues. In higher plants, most peroxidases are encoded by large, multigenic families that mainly originated from gene and chromosomal duplications.• Using phylogenetic, genomic and functional analyses, we have identified and characterized a new class of putative heme peroxidases, called ascorbate peroxidase-related (APx-R), which arose specifically in the lineage of plants.• The APx-R protein is structurally related to the ascorbate peroxidases, although the active site contains many conserved substitutions. Unlike all other plant peroxidases, which are encoded by gene families, APx-R is encoded by a single-copy gene in virtually all the species analyzed. APx-R proteins are targeted to the chloroplast and can physically interact with chloroplastic APx proteins. APx-Rknockdown rice (Oryza sativa) plants presented delayed development and a disturbed steady state of the antioxidant system compared with wild type. Moreover, the accumulation of APx-R transcripts was modulated by drought, UV irradiation, cold, and aluminum exposure in rice, suggesting the involvement of APx-R in the environmental stress response.• Our results reveal the existence of a new class of heme peroxidase which seems to play a role in the antioxidant system in plants, probably by modulating the activity of chloroplastic APx proteins.

The gram-negative anaerobic gut bacterium Bilophila wadsworthia is the third most common isolate in perforated and gangrenous appendicitis, being also found in a variety of other infections. This organism performs a unique kind of anaerobic respiration in which taurine, a major organic solute in mammals, is used as a source of sulphite that serves as terminal acceptor for the electron transport chain. We show here that molecular hydrogen, one of the major products of fermentative bacteria in the colon, is an excellent growth substrate for B. wadsworthia. We have quantified the enzymatic activities associated with the oxidation of H(2), formate and pyruvate for cells obtained in different growth conditions. The cell extracts present high levels of hydrogenase activity, and up to five different hydrogenases can be expressed by this organism. One of the hydrogenases appears to be constitutive, whereas the others show differential expression in different growth conditions. Two of the hydrogenases are soluble and are recognised by antibodies against a [FeFe] hydrogenase of a sulphate reducing bacterium. One of these hydrogenases is specifically induced during fermentative growth on pyruvate. Another two hydrogenases are membrane-bound and show increased expression in cells grown with hydrogen. Further work should be carried out to reveal whether oxidation of hydrogen contributes to the virulence of B. wadsworthia.

Human α1-acid glycoprotein (AGP) is an abundant human plasma glycoprotein that may be N-glycosylated at five positions. AGP plays important roles on pharmacokinetics and can rise up to 5-fold in inflammatory events. In such events, the glycan chains attached to Asn54, Asn75 and Asn85 may become fucosylated, originating a sialyl-Lewis X epitope. This epitope, in turn, can bind selectin proteins. Such interplay is important for immunomodulation. While the X-ray structure of unglycosylated AGP has been reported, the absence of the glycan chains hampered the further insights into its structural biology and, ultimately, into its biological function. Thus, the current work intends to contribute in the characterization of the structural glycobiology and function of AGP by building a structural model of its fully glycosylated form, taking into account the different glycoforms that are found in vivo. The obtained data points to the absence of a major influence of glycosylation on AGP's secondary structure, in agreement with crystallography observations. However, the glycan chains seem able to interfere with the protein dynamics, mainly at the AGP-ligand-binding site, indicating a possible role in its complexation to drugs and other bioactive compounds. By examining the influence of fucosylation on AGP structure and binding to selectins, it is proposed that the latter may bind to glycan chains linked to Asn54 and Asn75, and that this binding may involve other glycans, such as the one attached to Asn15. These results point to an increased participation of carbohydrates on the observed AGP roles in pharmacokinetics and inflammation.

No abstract