N-Terminal pyroglutamate formation of Aβ38 and Aβ40 enforces oligomer formation and potency to disrupt hippocampal long-term potentiation

Pyroglutamate (pGlu)-modified amyloid peptides have been identified in sporadic and familial forms of Alzheimer's disease (AD) and the inherited disorders familial British and Danish Dementia (FBD and FDD). In this study, we characterized the aggregation of amyloid-β protein Aβ37, Aβ38, Aβ40, Aβ42 and ADan species in vitro, which were modified by N-terminal pGlu (pGlu-Aβ3-x, pGlu-ADan) or possess the intact N-terminus (Aβ1-x, ADan). The pGlu-modification confers rapid formation of oligomers and short fibrillar aggregates. In accordance with these observations, the pGlu-modified Aβ38, Αβ40 and Αβ42 species inhibit hippocampal long term potentiation of synaptic response, but pGlu-Aβ3-42 showing the highest effect. Among the unmodified Aβ peptides, only Aβ1-42 exhibites such propensity, which was similar to pGlu-Aβ3-38 and pGlu-Aβ3-40. Likewise, the amyloidogenic peptide pGlu-ADan impaired synaptic potentiation more pronounced than N-terminal unmodified ADan. The results were validated using conditioned media from cultivated HEK293 cells, which express APP variants favoring the formation of Aβ1-x, Aβ3-x or N-truncated pGlu-Aβ3-x species. Hence, we show that the ability of different amyloid peptides to impair synaptic function apparently correlates to their potential to form oligomers as a common mechanism. The pGlu-modification is apparently mediating a higher surface hydrophobicity, as shown by 1-anilinonaphtalene-8-sulfonate fluorescence, which enforces potential to interfere with neuronal physiology.     

Drosophila neuroglian: a member of the immunoglobulin superfamily with extensive homology to the vertebrate neural adhesion molecule L1

Drosophila neuroglian is an integral membrane glycoprotein that is expressed on a variety of cell types in the Drosophila embryo, including expression on a large subset of glial and neuronal cell bodies in the central and peripheral nervous systems and on the fasciculating axons that extend along them. Neuroglian cDNA clones were isolated by expression cloning. cDNA sequence analysis reveals that neuroglian is a member of the immunoglobulin superfamily. The extracellular portion of the protein consists of six immunoglobulin C2-type domains followed by five fibronectin type III domains. Neuroglian is closely related to the immunoglobulin-like vertebrate neural adhesion molecules and, among them, shows most extensive homology to mouse L1. Its homology to L1 and its embryonic localization suggest that neuroglian may play a role in neural and glial cell adhesion in the developing Drosophila embryo. We report here on the identification of a lethal mutation in the neuroglian gene.     

Fiber‐type composition in the perivertebral musculature of lizards: Implications for the evolution of the diapsid trunk muscles

The perivertebral musculature of lizards is critical for the stabilization and the mobilization of the trunk during locomotion. Some trunk muscles are also involved in ventilation. This dual function of trunk muscles in locomotion and ventilation leads to a biomechanical conflict in many lizards and constrains their ability to breathe while running (“axial constraint”) which likely is reflected by their high anaerobic scope. Furthermore, different foraging and predator‐escape strategies were shown to correlate with the metabolic profile of locomotor muscles in lizards. Because knowledge of muscle's fiber‐type composition may help to reveal a muscle's functional properties, we investigated the distribution pattern of muscle fiber types in the perivertebral musculature in two small lizard species with a generalized body shape and subjected to the axial constraint (Dipsosaurus dorsalis, Acanthodactylus maculatus) and one species that circumvents the axial constraint by means of gular pumping (Varanus exanthematicus). Additionally, these species differ in their predator‐escape and foraging behaviors. Using refined enzyme‐histochemical protocols, muscle fiber types were differentiated in serial cross‐sections through the trunk, maintaining the anatomical relationships between the skeleton and the musculature. The fiber composition in Dipsosaurus and Acanthodactylus showed a highly glycolytic profile, consistent with their intermittent locomotor style and reliance on anaerobic metabolism during activity. Because early representatives of diapsids resemble these two species in several postcranial characters, we suggest that this glycolytic profile represents the plesiomorphic condition for diapsids. In Varanus, we found a high proportion of oxidative fibers in all muscles, which is in accordance with its high aerobic scope and capability of sustained locomotion. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Amino acid sequence of the N-terminus and selected tryptic peptides of the active subunit of human plasma carboxypeptidase N: comparison with other carboxypeptidases

Human plasma carboxypeptidase N was purified to homogeneity and its active and inactive subunits were separated. By introducing a novel technique, both forms of the active subunit (Mr = 55,000 and Mr = 48,000) were isolated. N-terminal sequencing of the active subunit of human carboxypeptidase N revealed significant homology with the N-terminal sequence of bovine carboxypeptidase H (43% identity) and to a lesser extent with carboxypeptidase A (29% identity) or carboxypeptidase B (18% identity). The active subunit of carboxypeptidase N was hydrolyzed with trypsin and 4 of the tryptic peptides were isolated by HPLC and sequenced. The sequences of the four peptides were homologous (39-64% identity) with regions of carboxypeptidase H corresponding to the middle (residues 148-175) and C-terminal portion (residues 321-408). These regions had essentially no homology with carboxypeptidase A or B. These data indicate that carboxypeptidase H and the active subunit of carboxypeptidase N may have diverged from a common ancestral gene.     

RESTRICTION FRAGMENT ANALYSIS OF CHLOROPLAST DNA AND THE SYSTEMATICS OF VIGUIERA AND RELATED GENERA (ASTERACEAE: HELIANTHEAE)

Phylogenetic relationships among 31 species representing variously Helianthus, Helianthopsis, Heliomeris, Simsia, Viguiera, and Tithonia were assessed by chloroplast DNA restriction site mapping. A total of 147 mutations including 92 informative ones was detected using 16 restriction enzymes, with an estimated sequence divergence within the group of 1.4%. Parsimony analysis produced a single most parsimonious tree with a length of 161 steps and a consistency index of 0.91. Statistically significant clades, as assessed by the bootstrap method, correspond to a number of taxa recognized previously, including Helianthus (3 species), Helianthopsis (5 species), and several groups within Viguiera, including sect. Maculatae (4 species), the Baja California group (6 species), sect. Paradosa (2 species) and V. dentata (3 samples). However, species of Viguiera collectively form a highly paraphyletic group relative to species of other genera. Helianthus and Helianthopsis were separated into different clades, supporting their recent segregation. Placement of H. porteri in Helianthus rather than Heliomeris was confirmed; the single sample of the latter genus was most similar to the Baja California group of Viguiera. An expected relationship between Simsia (2 species) and one member of Viguiera ser. Grammatoglossae was confirmed (although not with two other putatively related members of Viguiera) and an unexpected relationship between Simsia and Tithonia was suggested. The presence of Mexican taxa as the more basal groups in the tree points toward a possible Mexican origin for Viguiera and related genera. A molecular clock hypothesis is rejected in many pairwise comparisons involving woody taxa with herbaceous ones, although it could not be rejected in most pairwise comparisons involving taxa of similar habit.