The molecular genetics of schizophrenia: an emerging consensus

Schizophrenia is perhaps the most debilitating mental disease and determining the underlying cause has become a challenging area of psychiatric research. It is relatively well established that genes play a role in the aetiology of schizophrenia. In this article, a review of important findings related to schizophrenia as a genetic trait will be provided, including a discussion of family, twin and adoption studies. Molecular genetic studies of specific candidate genes are then reviewed. Some controversies within the literature are examined and possible directions for future research are discussed.     

On the interaction of colicin E3 with the ribosome

Colicin E3 is a protein that kills Escherichia coli cells by a process that involves binding to a surface receptor, entering the cell and inactivating its protein biosynthetic machinery. Colicin E3 kills cells by a catalytic mechanism of a specific ribonucleolytic cleavage in 16S rRNA at the ribosomal decoding A-site between A1493 and G1494 (E. coli numbering system). The breaking of this single phosphodiester bond results in a complete cessation of protein biosynthesis and cell death. The inactive E517Q mutant of the catalytic domain of colicin E3 binds to 30S ribosomal subunits of Thermus thermophilus, as demonstrated by an immunoblotting assay. A model structure of the complex of the ribosomal subunit 30S and colicin E3, obtained via docking, explains the role of the catalytic residues, suggests a catalytic mechanism and provides insight into the specificity of the reaction. Furthermore, the model structure suggests that the inhibitory action of bound immunity is due to charge repulsion of this acidic protein by the negatively charged rRNA backbone     

Ferritin,iron homeostasis,and oxidative damage

Ferritin is one of the major proteins of iron metabolism. It is almost ubiquitous and tightly regulated by the metal. Biochemical and structural properties of the ferritins are largely conserved from bacteria to man, although the role in the regulation of iron trafficking varies in the different organisms. Recent studies have clarified some of the major aspects of the reaction between iron and ferritin, which results in the formation of the iron core and production of hydrogen peroxide. The characterization of cellular models in which ferritin expression is modulated has shown that the ferroxidase catalytic site on the H-chain has a central role in regulating iron availability. In turn, this has secondary effects on a number of cellular activities, which include proliferation and resistance to oxidative damage. Moreover, the response to apoptotic stimuli is affected by H-ferritin expression. Altered ferritin L-chain expression has been found in at least two types of genetic disorders, although its role in the determination of the pathology has not been fully clarified. The recent discovery of a new ferritin specific for the mitochondria, which is functionally similar to the H-ferritin, opens new perspectives in the study of the relationships between iron, oxidative damage and free radicals.     

Gurken, a TGF-alpha-like protein involved in axis determination in Drosophila, directly binds to the EGF-receptor homolog Egfr

The establishment of axial polarity in the Drosophila egg and embryo depends on intercellular communication between two cell types in the ovary, the germline, and the soma. The genes gurken and egfr encode two essential players of this communication pathway. Gurken protein, a TGF-alpha-like molecule, is expressed in the germline, while the EGF-receptor homolog, Egfr, is expressed in the somatic cells of the ovary. Using the yeast two-hybrid system we show here, for the first time, that Gurken protein directly binds to the extracellular domain of Egfr. This direct physical association requires the presence of an intact EGF motif within Gurken protein. Furthermore, we provide evidence that this characteristic motif may be sufficient for interaction with the receptor, at list in vitro. Our results firmly establish Gurken as the germline ligand of Drosophila Egfr.     

Molecular basis for expression of common and rare fragile sites

Fragile sites are specific loci that form gaps, constrictions, and breaks on chromosomes exposed to partial replication stress and are rearranged in tumors. Fragile sites are classified as rare or common, depending on their induction and frequency within the population. The molecular basis of rare fragile sites is associated with expanded repeats capable of adopting unusual non-B DNA structures that can perturb DNA replication. The molecular basis of common fragile sites was unknown. Fragile sites from R-bands are enriched in flexible sequences relative to nonfragile regions from the same chromosomal bands. Here we cloned FRA7E, a common fragile site mapped to a G-band, and revealed a significant difference between its flexibility and that of nonfragile regions mapped to G-bands, similar to the pattern found in R-bands. Thus, in the entire genome, flexible sequences might play a role in the mechanism of fragility. The flexible sequences are composed of interrupted runs of AT-dinucleotides, which have the potential to form secondary structures and hence can affect replication. These sequences show similarity to the AT-rich minisatellite repeats that underlie the fragility of the rare fragile sites FRA16B and FRA10B. We further demonstrate that the normal alleles of FRA16B and FRA10B span the same genomic regions as the common fragile sites FRA16C and FRA10E. Our results suggest that a shared molecular basis, conferred by sequences with a potential to form secondary structures that can perturb replication, may underlie the fragility of rare fragile sites harboring AT-rich minisatellite repeats and aphidicolin-induced common fragile sites.     

The selenoprotein GPX4 is essential for mouse development and protects from radiation and oxidative damage insults

Lipid peroxidation has been implicated in a variety of pathophysiological processes, including inflammation, atherogenesis, neurodegeneration, and the ageing process. Phospholipid hydroperoxide glutathione peroxidase (GPX4) is the only major antioxidant enzyme known to directly reduce phospholipid hydroperoxides within membranes and lipoproteins, acting in conjunction with alpha tocopherol (vitamin E) to inhibit lipid peroxidation. Here we describe the generation and characterization of GPX4-deficient mice by targeted disruption of the murine Gpx4 locus through homologous recombination in embryonic stem cells. Gpx4(-/-) embryos die in utero by midgestation (E7.5) and are associated with a lack of normal structural compartmentalization. Gpx4(+/-) mice display reduced levels of Gpx4 mRNA and protein in various tissues. Interestingly, cell lines derived from Gpx4(+/-) mice are markedly sensitive to inducers of oxidative stress, including gamma-irradiation, paraquat, tert-butylhydroperoxide, and hydrogen peroxide, as compared to cell lines derived from wild-type control littermates. Gpx4(+/-) mice also display reduced survival in response to gamma-irradiation. Our observations establish GPX4 as an essential antioxidant enzyme in mice and suggest that it performs broad functions as a component of the mammalian antioxidant network.     

The Principal Neutralizing Determinant of HIV-1IIIB: Conformation of the Peptide Bound to a Neutralizing Antibody Studied by 2D-NMR

RP135 is a 24-residue peptide corresponding to the principal neutralizing determinant of the envelope glycoprotein gp120 of the human immunodeficiency virus type 1. We have studied the conformation of RP135 in complex with a neutralizing antibody 0.5 raised against gp120 by 2D NMR spectroscopy. The antigenic determinant recognized by this antibody was mapped using a combination of HOHAHA and ROESY measurements, in which resonances of the Fab and the tightly bound peptide residues are eliminated and the mobile residues of the bound peptide are sequentially assigned. We found that residues Ser⁶ - Thr¹⁹ are part of the epitope, while Lys⁵ and Ile²⁰ are at its boundaries. Difference spectroscopy was applied to study the conformation of the bound peptide representing the epitope within the 52 kDa of the Fab complex. Specific residues of the peptide were deuterated or replaced and the difference between the NOESY spectrum of the complex with the unlabeled residue and the NOESY spectrum of the complex with the modified residue revealed the interactions of the labeled residue both within the peptide and with the Fab fragment. A total of 122 distance restraints derived from the difference spectra enabled the calculation of the structure of the bound peptide. The peptide forms a 10-residue loop, while the two segments flanking this loop interact extensively with each other and possibly form anti-parallel -strands. The loop conformation could be observed due to the unusual large size (17 residues) of the antigenic determinant recognized by 0.5.