Neuroglobin and cytoglobin. Fresh blood for the vertebrate globin family.
(33/224)
Neuroglobin and cytoglobin are two recently discovered members of the vertebrate globin family. Both are intracellular proteins endowed with hexacoordinated heme-Fe atoms, in their ferrous and ferric forms, and display O2 affinities comparable with that of myoglobin. Neuroglobin, which is predominantly expressed in nerve cells, is thought to protect neurons from hypoxic-ischemic injury. It is of ancient evolutionary origin, and is homologous to nerve globins of invertebrates. Cytoglobin is expressed in many different tissues, although at varying levels. It shares common ancestry with myoglobin, and can be traced to early vertebrate evolution. The physiological roles of neuroglobin and cytoglobin are not completely understood. Although supplying cells with O2 is the likely function, it is also possible that both globins act as O2-consuming enzymes or as O2 sensors. Here, we review what is currently known about neuroglobin and cytoglobin in terms of their function, tissue distribution and relatedness to the well-known hemoglobin and myoglobin. Strikingly, the data reveal that O2 metabolism in cells is more complicated than was thought before, requiring unexpected O2-binding proteins with potentially novel functional features. (+info)
Expression and localization of carbonic anhydrase and ATPases in the symbiotic tubeworm Riftia pachyptila.
(34/224)
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. (+info)
The loss of the hemoglobin H2S-binding function in annelids from sulfide-free habitats reveals molecular adaptation driven by Darwinian positive selection.
(35/224)
The hemoglobin of the deep-sea hydrothermal vent vestimentiferan Riftia pachyptila (annelid) is able to bind toxic hydrogen sulfide (H(2)S) to free cysteine residues and to transport it to fuel endosymbiotic sulfide-oxidising bacteria. The cysteine residues are conserved key amino acids in annelid globins living in sulfide-rich environments, but are absent in annelid globins from sulfide-free environments. Synonymous and nonsynonymous substitution analysis from two different sets of orthologous annelid globin genes from sulfide rich and sulfide free environments have been performed to understand how the sulfide-binding function of hemoglobin appeared and has been maintained during the course of evolution. This study reveals that the sites occupied by free-cysteine residues in annelids living in sulfide-rich environments and occupied by other amino acids in annelids from sulfide-free environments, have undergone positive selection in annelids from sulfide-free environments. We assumed that the high reactivity of cysteine residues became a disadvantage when H(2)S disappeared because free cysteines without their natural ligand had the capacity to interact with other blood components, disturb homeostasis, reduce fitness and thus could have been counterselected. To our knowledge, we pointed out for the first time a case of function loss driven by molecular adaptation rather than genetic drift. If constraint relaxation (H(2)S disappearance) led to the loss of the sulfide-binding function in modern annelids from sulfide-free environments, our work suggests that adaptation to sulfide-rich environments is a plesiomorphic feature, and thus that the annelid ancestor could have emerged in a sulfide-rich environment. (+info)
Comparison of Artificial Neural Network (ANN) Model Development Methods for Prediction of Macroinvertebrate Communities in the Zwalm River Basin in Flanders, Belgium.
(36/224)
Modelling has become an interesting tool to support decision making in water management. River ecosystem modelling methods have improved substantially during recent years. New concepts, such as artificial neural networks, fuzzy logic, evolutionary algorithms, chaos and fractals, cellular automata, etc., are being more commonly used to analyse ecosystem databases and to make predictions for river management purposes. In this context, artificial neural networks were applied to predict macroinvertebrate communities in the Zwalm River basin (Flanders, Belgium). Structural characteristics (meandering, substrate type, flow velocity) and physical and chemical variables (dissolved oxygen, pH) were used as predictive variables to predict the presence or absence of macroinvertebrate taxa in the headwaters and brooks of the Zwalm River basin. Special interest was paid to the frequency of occurrence of the taxa as well as the selection of the predictors and variables to be predicted on the prediction reliability of the developed models. Sensitivity analyses allowed us to study the impact of the predictive variables on the prediction of presence or absence of macroinvertebrate taxa and to define which variables are the most influential in determining the neural network outputs. (+info)
Rhodotorula benthica sp. nov. and Rhodotorula calyptogenae sp. nov., novel yeast species from animals collected from the deep-sea floor, and Rhodotorula lysiniphila sp. nov., which is related phylogenetically.
(37/224)
Three novel species of the genus Rhodotorula are described. Rhodotorula benthica sp. nov. (type strain JCM 10901(T) = SY-91(T)) and Rhodotorula calyptogenae sp. nov. (type strain JCM 10899(T) = SY-86(T)) were respectively isolated from the tubeworm Lamellibrachia sp. and the giant white clam Calyptogena sp., collected from the deep-sea floor of the Pacific Ocean off Japan. Rhodotorula lysiniphila sp. nov. (type strain JCM 5951(T)) is proposed for strains isolated previously in Japan and Pakistan. The three species were placed phylogenetically into a species complex comprising Rhodotorula laryngis, Rhodotorula minuta, Rhodotorula pallida and Rhodotorula slooffiae. R. minuta and R. slooffiae are closely related in both the D1/D2 region of the 26S rDNA and the internal transcribed spacer and 5.8S rDNA regions. R. benthica and R. laryngis were closer to R. pallida based on the D1/D2 region. Other relationships were not clear. (+info)
The directionality of chitin biosynthesis: a revisit.
(38/224)
The molecular directionality of chitin biosynthesis was investigated by transmission electron microscopy (TEM) using electron crystallography methods applied to reducing-end-labelled beta-chitin microcrystals from vestimentiferan Lamellibrachia satsuma tubes and nascent beta-chitin microfibrils from the diatom Thalassiosira weissflogii. The data allowed confirmation that the microfibrils were extruded with their reducing end away from the biosynthetic loci, an orientation consistent only with elongation through polymerization at the non-reducing end of the growing chains. Such a chain-extension mechanism, which has also been demonstrated for cellulose and hyaluronan, appears to be general for glycosyltransferases that belong to the GT2 (glycosyl transferase 2) family. The data also allowed confirmation that in beta-chitin the chains are crystallized in a 'parallel-up' mode, in contrast with hypotheses proposed in previous reports. (+info)
Mechanism of fluorescence and conformational changes of the sarcoplasmic calcium binding protein of the sand worm Nereis diversicolor upon Ca2+ or Mg2+ binding.
(39/224)
The calcium-binding protein isolated from the sarcoplasm of the muscles of the sand worm Nereis diversicolor has four EF-hands and three active binding sites for Ca(2+) or Mg(2+). Nereis diversicolor sarcoplasmic calcium-binding protein contains three tryptophan residues at positions 4, 57, and 170, respectively. The Wt protein shows a very limited fluorescence increase upon binding of Ca(2+) or Mg(2+). Single-tryptophan-containing mutants were produced and purified. The fluorescence titrations of these mutants show a limited decrease of the affinity for calcium, but no alterations of the cooperativity. Upon adding calcium, Trp170 shows a strong fluorescence increase, Trp57 an extensive fluorescence decrease, and Trp4 shows no fluorescence change. Therefore mutant W4F/W170F is ideally suited to analyze the fluorescence titrations and to study the binding mechanism. Mutations of the calcium ligands at the z-position in the three binding sites show no effect at site I and a total loss of cooperativity at sites III and IV. The quenching of Trp57 upon calcium binding is dependent on the presence of arginine R25, but this residue is not just a simple dynamic quencher. The role of the salt bridge R25-D58 is also investigated. (+info)
Changes in the spermatozoon during fertilization in Hydroides hexagonus (Annelida). I. Passage of the acrosomal region through the vitelline membrane.
(40/224)
In the previous paper the structure of the acrosomal region of the spermatozoon was described. The present paper describes the changes which this region undergoes during passage through the vitelline membrane. The material used consisted of moderately polyspermic eggs of Hydroides hexagonus, osmium-fixed usually 9 seconds after insemination. There are essentially four major changes in the acrosome during passage of the sperm head through the vitelline membrane. First, the acrosome breaks open apically by a kind of dehiscence which results in the formation of a well defined orifice. Around the lips of the orifice the edges of the plasma and acrosomal membranes are then found to be fused to form a continuous membranous sheet. Second, the walls of the acrosomal vesicle are completely everted, and this appears to be the means by which the apex of the sperm head is moved through the vitelline membrane. The lip of the orifice comes to lie deeper and deeper within the vitelline membrane. At the same time the lip itself is made up of constantly changing material as first the material of the outer zone and then that of the intermediate zone everts. One is reminded of the lip of an amphibian blastopore, which during gastrulation maintains its morphological identity as a lip but is nevertheless made up of constantly changing cells, with constantly changing outline and even constantly changing position. Third, the large acrosomal granule rapidly disappears. This disappearance is closely correlated with a corresponding disappearance of a part of the principal material of the vitelline membrane from before it, and the suggestion is made that the acrosomal granule is the source of the lysin which dissolves this part of the vitelline membrane. Fourth, in the inner zone the fifteen or so short tubular invaginations of the acrosomal membrane, present in the normal unreacted spermatozoon, lengthen considerably to become a tuft of acrosomal tubules. These tubules are the first structures of the advancing sperm head to touch the plasma membrane of the egg. It is notable that the surface of the acrosomal tubules which once faced into the closed acrosomal cavity becomes the first part of the sperm plasma membrane to meet the plasma membrane of the egg. The acrosomal tubules of Hydroides, which arise simply by lengthening of already existing shorter tubules, are considered to represent the acrosome filaments of other species. (+info)