Cloning and characterization of Arenicola marina peroxiredoxin 6, an annelid two-cysteine peroxiredoxin highly homologous to mammalian one-cysteine peroxiredoxins.

Peroxiredoxins (PRDXs) are a superfamily of thiol-dependent peroxidases found in all phyla. PRDXs are mechanistically divided into three subfamilies, namely typical 2-Cys, atypical 2-Cys, and 1-Cys PRDXs. To reduce peroxides, the N-terminal peroxidatic Cys of PRDXs is first oxidized into sulfenic acid. This intermediate is reduced by forming a disulfide bond either with a resolving Cys of another monomeric entity (typical 2-Cys) or of the same molecule (atypical 2-Cys). In 1-Cys PRDXs, the resolving Cys is missing and the sulfenic acid of the peroxidatic Cys is reduced by a heterologous thiol-containing reductant. In search of a homolog of human 1-Cys PRDX6 in Arenicola marina, an annelid worm living in intertidal sediments, we have cloned and characterized a PRDX exhibiting high sequence homology with its mammalian counterpart. However, A. marina PRDX6 possesses five Cys among which two Cys function as peroxidatic and resolving Cys of typical 2-Cys PRDXs. Thus, A. marina PRDX6 belongs to a transient group exhibiting sequence homologies with mammalian 1-Cys PRDX6 but must be mechanistically classified into typical 2-Cys PRDXs. Moreover, PRDX6 is highly expressed in tissues directly exposed to the external environment, suggesting that this PRDX may be of particular importance for protection against exogenous oxidative attacks.

Expression and localization of carbonic anhydrase and ATPases in the symbiotic tubeworm Riftia pachyptila.

The symbiotic tubeworm Riftia pachyptila needs to fuel its chemoautotrophic symbiotic bacteria with inorganic carbon. CO(2) is transported from the surrounding water to the bacteriocytes located in the trophosome, through the branchial plume and the body fluids. Previous studies have demonstrated the implication of carbonic anhydrase (CA) and proton pumps (ATPases) at various steps of CO(2) transport. The present study describes the expression pattern of cytosolic CA using an RNA probe and its histochemical and immunocytochemical localization in the trophosome and branchial plume of RIFTIA: Immunolocalization of V-H(+)ATPase and Na(+)K(+)-ATPase were also performed and related to CA localization. In the branchial plume, CA is expressed and localized in the most apical region of the branchial epithelium, close to the surrounding water. V-H(+)ATPase is mostly colocalized with CA and both enzymes probably allow CO(2) entry against the concentration gradient while regulating intracellular pH. Na(+)K(+)-ATPase is mostly restricted to the basal part of epithelial cells and probably participates in CO(2) transport to the body fluids. In the trophosome lobules, cytosolic CA is expressed and found in bacteriocytes and peritoneal cells. Hypotheses on the role of CA in bicarbonate and CO(2) interconversion to fuel the symbiotic bacteria are discussed.