Agrin isoforms and their role in synaptogenesis.

Agrin is thought to mediate the motor neuron-induced aggregation of synaptic proteins on the surface of muscle fibers at neuromuscular junctions. Recent experiments provide direct evidence in support of this hypothesis, reveal the nature of agrin immunoreactivity at sites other than neuromuscular junctions, and have resulted in findings that are consistent with the possibility that agrin plays a role in synaptogenesis throughout the nervous system.     

Correlation between in vitro stability and in vivo performance of anti-GCN4 intrabodies as cytoplasmic inhibitors

A cellular assay system for measuring the activity of cytoplasmically expressed anti-GCN4 scFv fragments directed against the Gcn4p dimerization domain was established in the budding yeast Saccharomyces cerevisiae. The inhibitory potential of different constitutively expressed anti-GCN4 scFv intrabodies was monitored by measuring the activity of beta-galactosidase expressed from a GCN4-dependent reporter gene. The in vivo performance of these scFv intrabodies in specifically decreasing reporter gene activity was related to their in vitro stability, measured by denaturant-induced equilibrium unfolding. A framework-engineered stabilized version showed significantly improved activity, while a destabilized point mutant of the anti-GCN4 wild-type showed decreased effects in vivo. These results indicate that stability engineering can result in improved performance of scFv fragments as intrabodies. Increasing the thermodynamic stability appears to be an essential factor for improving the yield of functional scFv in the reducing environment of the cytoplasm, where the conserved intradomain disulfides of antibody fragments cannot form.     

Detection and identification of protein interactions of S100 proteins by ProteinChip technology

The aim of this work was to establish an approach for identification of protein interactions. This assay used an anti-S100A8 antibody coupled on beads and incubated with cell extract. The bead eluates were analyzed using ProteinChip technology and subsequently subjected to an appropriate digestion. Molecular masses of digestion fragments were determined by SELDI-MS, and database analysis revealed S100A10 as interacting protein. This result was confirmed by co-immunoprecipitation and immunocapturing. Using S100A10 as new bait, a specific interaction with S100A7 was detectable.     

A relationship between cerebellar Purkinje cells and spatial working memory demonstrated in a lurcher/chimera mouse model system

New emphasis has been placed upon cerebellar research because of recent reports demonstrating involvement of the cerebellum in non-motor cognitive behaviors. Included in the growing list of cognitive functions associated with cerebellar activation is working memory. In this study, we explore the potential role of the cerebellum in spatial working memory using a mouse model of Purkinje cell loss. Specifically, we make aggregation chimeras between heterozygous lurcher (Lc/+) mutant embryos and +/+ (wildtype) embryos and tested them in the delayed matching-to-position (DMTP) task. Lc/+ mice lose 100% of their Purkinje cells postnatally due to a cell-intrinsic gain-of-function mutation. Lc/+<->+/+ chimeras therefore have Purkinje cells ranging from 0 to normal numbers. Through histological examination of chimeric mice and observations of motor ability, we showed that ataxia is dependent upon both the number and distribution of Purkinje cells in the cerebellum. In addition, we found that Lc/+ mice, with a complete loss of Purkinje cells, have a generalized deficit in DMTP performance that is probably associated with their motor impairment. Finally, we found that Lc/+<->+/+ chimeric mice, as a group, did not differ from control mice in this task. Rather, surprisingly, analysis of their total Purkinje cells and performance in the DMTP task revealed a significant negative relationship between these two variables. Together, these findings indicate that the cerebellum plays a minor or indirect role in spatial working memory.     

Anti-substance P anti-idiotypic antibodies. Characterization and biological activities

Antibodies to substance P (SP) produced in rabbits have been characterized for their specificity toward SP and some 30 SP-related peptides. For each compound, we observed a close correlation between capacity of binding to anti-SP antibodies and biological activity, namely their spasmogenic effect on guinea pig ileum in vitro and their hypotensive effect in the rat in vivo, indicating that the combining sites of anti-SP and SP receptor(s) are structurally very similar. Further immunization of five rabbits with anti-SP immunoglobulins elicited in two allotype-matched animals the production of anti-SP anti-idiotypic antibodies. These latter antibodies were found to strongly inhibit the spasmogenic action of SP on the guinea pig ileum. In contrast, they specifically enhanced, like SP, phospholipid turnover in rat parotid gland cells, a physiological function mediated through an activation of SP receptors. Immunocytochemical studies actually revealed the presence of specific membranous binding sites for anti-idiotypic antibodies on the parotid gland-dissociated cells. The anti-idiotypic antibodies described here, which thus behave either as agonists or antagonists for SP depending on the biological test, might be used as original and powerful tools not only in studies of the receptor stereospecificity but also in attempts to purify the membranous SP receptors.     

Structural insights into fibronectin type III domain-mediated signaling

The alternatively spliced type III extradomain B (EIIIB) of fibronectin (FN) is expressed only during embryogenesis, wound healing and tumorigenesis. The biological function of this domain is unclear. We describe here the first crystal structure of the interface between alternatively spliced EIIIB and its adjacent FN type III domain 8 (FN B-8). The opened CC' loop of EIIIB, and the rotation and tilt of EIIIB allow good access to the FG loop of FN-8, which is normally hindered by the CC' loop of FN-7. In addition, the AGEGIP sequence of the CC' loop of EIIIB replaces the NGQQGN sequence of the CC' loop of FN-7. Finally, the CC' loop of EIIIB forms an acidic groove with FN-8. These structural findings warrant future studies directed at identifying potential binding partners for FN B-8 interface, linking EIIIB to skeletal and cartilaginous development, wound healing, and tumorigenesis, respectively.     

Solution structure of the human CC chemokine 2: A monomeric representative of the CC chemokine subtype.

HCC-2, a 66-amino acid residue human CC chemokine, was reported to induce chemotaxis on monocytes, T-lymphocytes, and eosinophils. The three-dimensional structure of HCC-2 has been determined by 1H nuclear magnetic resonance (NMR) spectroscopy and restrained molecular dynamics calculations on the basis of 871 experimental restraints. The structure is well-defined, exhibiting average root-mean-square deviations of 0.58 and 0.96 A for the backbone heavy atoms and all heavy atoms of residues 5-63, respectively. In contrast to most other chemokines, subtle structural differences impede dimer formation of HCC-2 in a concentration range of 0.1 microM to 2 mM. HCC-2, however, exhibits the same structural elements as the other chemokines, i.e., a triple-stranded antiparallel beta-sheet covered by an alpha-helix, showing that the chemokine fold is not influenced by quaternary interactions. Structural investigations with a HCC-2 mutant prove that a third additional disulfide bond present in wild-type HCC-2 is not necessary for maintaining the relative orientation of the helix and the beta-sheet.