Occurrence and functions of free D-aspartate and its metabolizing enzymes

L-Tyrosine Confers Residualizing Properties to a d-Amino Acid-Rich Residualizing Peptide for Radioiodination of Internalizing Antibodies

PURPOSE

The aims of the study were to develop and evaluate a novel residualizing peptide for labeling internalizing antibodies with (124)I to support clinical development using immuno-positron emission tomography (PET).

METHODS

The anti-epidermal growth factor receptor antibody ch806 was radiolabeled directly or indirectly with isotopes and various residualizing peptides. Azido-derivatized radiolabeled peptides were conjugated to dibenzylcyclooctyne-derivatized ch806 antibody via click chemistry. The radiochemical purities, antigen-expressing U87MG.de2-7 human glioblastoma cell-binding properties, and targeting of xenografts at 72 hours post injection of all radioconjugates were compared. Biodistribution of (124)I-PEG4-tptddYddtpt-ch806 and immuno-PET imaging were evaluated in tumor-bearing mice.

RESULTS

Biodistribution studies using xenografts at 72 hours post injection showed that (131)I-PEG4-tptddYddtpt-ch806 tumor uptake was similar to (111)In-CHX-A″-DTPA-ch806. (125)I-PEG4-tptddyddtpt-ch806 showed a lower tumor uptake value but higher than directly labeled (125)I-ch806. (124)I-PEG4-tptddYddtpt-ch806 was produced at 23% labeling efficiency, 98% radiochemical purity, 25.9 MBq/mg specific activity, and 64% cell binding in the presence of antigen excess. Tumor uptake for (124)I-PEG4-tptddYddtpt-ch806 was similar to (111)In-CHX-A″-DTPA-ch806. High-resolution immuno-PET/magnetic resonance imaging of tumors showed good correlation with biodistribution data.

CONCLUSIONS

The mixed d/l-enantiomeric peptide, dThr-dPro-dThr-dAsp-dAsp-Tyr-dAsp-dAsp-dThr-dPro-dThr, is suitable for radiolabeling antibodies with radiohalogens such as (124)I for high-resolution immuno-PET imaging of tumors and for evaluation in early-phase clinical trials.

Expression of biomass-degrading enzymes is a major event during conidium development in Trichoderma reesei

The conidium plays a critical role in the life cycle of many filamentous fungi, being the primary means for survival under unfavorable conditions. To investigate the transcriptional changes taking place during the transition from growing hyphae to conidia in Trichoderma reesei, microarray experiments were performed. A total of 900 distinct genes were classified as differentially expressed, relative to their expression at time zero of conidiation, at least at one of the time points analyzed. The main functional categories (FunCat) overrepresented among the upregulated genes were those involving solute transport, metabolism, transcriptional regulation, secondary metabolite synthesis, lipases, proteases, and, particularly, cellulases and hemicellulases. Categories overrepresented among the downregulated genes were especially those associated with ribosomal and mitochondrial functions. The upregulation of cellulase and hemicellulase genes was dependent on the function of the positive transcriptional regulator XYR1, but XYR1 exerted no influence on conidiation itself. At least 20% of the significantly regulated genes were nonrandomly distributed within the T. reesei genome, suggesting an epigenetic component in the regulation of conidiation. The significant upregulation of cellulases and hemicellulases during this process, and thus cellulase and hemicellulase content in the spores of T. reesei, contributes to the hypothesis that the ability to hydrolyze plant biomass is a major trait of this fungus enabling it to break dormancy and reinitiate vegetative growth after a period of facing unfavorable conditions.

Physiological evidence that D-aspartate activates a current distinct from ionotropic glutamate receptor currents in Aplysia californica neurons

D-Aspartate (D-Asp) activates an excitatory current in neurons of Aplysia californica. Although D-Asp is presumed to activate a subset of L-glutamate (L-Glu) channels, the identities of putative d-Asp receptors and channels are unclear. Whole cell voltage- and current-clamp studies using primary cultures of Aplysia buccal S cluster (BSC) neurons were executed to characterize D-Asp-activated ion channels. Both D-Asp and L-Glu evoked currents with similar current-voltage relationships, amplitudes, and relatively slow time courses of activation and inactivation when agonists were pressure applied. D-Asp-induced currents, however, were faster and desensitized longer, requiring 40 s to return to full amplitude. Of cells exposed to both agonists, 25% had D-Asp- but not L-Glu-induced currents, suggesting a receptor for D-Asp that was independent of l-Glu receptors. D-Asp channels were permeable to Na(+) and K(+), but not Ca²⁺, and were vulnerable to voltage-dependent Mg²⁺ block similarly to vertebrate NMDA receptor (NMDAR) channels. d-Asp may activate both NMDARs and non-l-Glu receptors in the nervous system of Aplysia.

D-aspartate oxidase localisation in pituitary and pineal glands of the female pig

Recent evidence has shown that D-aspartate modulates hormone secretion in the vertebral neuroendocrine system. Because only D-aspartate oxidase (DDO) can degrade D-aspartate, we determined DDO localisation in the pituitary and pineal glands to elucidate the control mechanisms of local D-aspartate concentration. Brain tissues and pituitary and pineal glands of the female pigs contained a similar DDO activity of 0.38-0.66 U/g protein. However, approximately ten-fold higher concentrations of D-aspartate (0.27-0.35 μmol/g protein) were found in both glands. To determine the distribution of immunoreactive DDO, we made a rabbit polyclonal antibody specific to porcine DDO using a recombinant porcine enzyme. DDO immunoreactivity was found in the cytoplasm of a subgroup of cells in the anterior and intermediate lobes, in a part of nerve processes and terminals in the posterior lobe, and in the cytoplasm of a small group of pinealocytes. We used dual-label immunocytochemistry to determine which pituitary hormones colocalise with DDO, and whether DDO and D-aspartate immunoreactivity is reciprocal. In the pituitary gland, almost all proopiomelanocortin-positive cells colocalised DDO, whereas only growth hormone-positive cells colocalised D-aspartate. D-aspartate immunoreactivity was not detected where DDO immunoreactivity was found. The present study suggests that DDO plays important roles to prevent undesirable off-target action of D-aspartate by strictly controlling local D-aspartate concentration in the pituitary and pineal glands.

D-amino acids in the brain: structure and function of pyridoxal phosphate-dependent amino acid racemases

D-serine serves as a co-agonist of the N-methyl D-aspartate receptor in mammalian brains, and its behavior is probably related to neurological disorders such as schizophrenia, Alzheimer's disease and amyotrophic lateral sclerosis. D-Serine is synthesized by a pyridoxal 5'-phosphate (PLP)-dependent serine racemase. In this minireview, we provide a detailed discussion on the reaction mechanism of the PLP-dependent amino acid racemase on the basis of its 3D structure. We compared the eukaryotic serine racemase with bacterial alanine racemase, the best-studied enzyme among the PLP-dependent amino acid racemases, and thus suggested a putative reaction mechanism for mammalian D-serine synthesis.