Environmental Pressure May Change the Composition Protein Disorder in Prokaryotes

Many prokaryotic organisms have adapted to incredibly extreme habitats. The genomes of such extremophiles differ from their non-extremophile relatives. For example, some proteins in thermophiles sustain high temperatures by being more compact than homologs in non-extremophiles. Conversely, some proteins have increased volumes to compensate for freezing effects in psychrophiles that survive in the cold. Here, we revealed that some differences in organisms surviving in extreme habitats correlate with a simple single feature, namely the fraction of proteins predicted to have long disordered regions. We predicted disorder with different methods for 46 completely sequenced organisms from diverse habitats and found a correlation between protein disorder and the extremity of the environment. More specifically, the overall percentage of proteins with long disordered regions tended to be more similar between organisms of similar habitats than between organisms of similar taxonomy. For example, predictions tended to detect substantially more proteins with long disordered regions in prokaryotic halophiles (survive high salt) than in their taxonomic neighbors. Another peculiar environment is that of high radiation survived, e.g. by Deinococcus radiodurans. The relatively high fraction of disorder predicted in this extremophile might provide a shield against mutations. Although our analysis fails to establish causation, the observed correlation between such a simplistic, coarse-grained, microscopic molecular feature (disorder content) and a macroscopic variable (habitat) remains stunning.     

Sarafotoxin receptors mediate phosphoinositide hydrolysis in various rat brain regions

Sarafotoxin-b, a potent snake vasoconstrictor peptide homologous to the mammalian endothelial vasoconstrictor endothelin, induces phosphoinositide (PI) hydrolysis in various brain regions of the rat. Sarafotoxin-b induced PI hydrolysis is largely independent of extracellular Ca2+ and is detected in all brain regions where toxin-binding sites are found. These results point to the existence of a hitherto undetected neuroreceptor associated with the PI cycle.     

Immunological and structural characterization of sarafotoxin/endothelin family of peptides

A highly specific and sensitive radioimmunoassay (RIA) was developed for the potent vasoconstrictor peptides, sarafotoxin-b and human endothelin. The antigenic determinants of the antibodies employed in studies with these assays were found to be localized within the amino acid sequence at positions 4-7. This was confirmed by CNBr cleavage of the methionyl residue at position 6 in the sarafotoxin and at position 7 in the endothelin. The chemically characterized modified peptides showed very low cross reactivity in the RIAs. On the other hand, the binding properties as well as the ability to induce phosphoinositide hydrolysis were very similar in the modified and native peptides, indicating that despite cleavage of the peptide bond the biologically active conformation responsible for either binding or phosphoinositide hydrolysis is retained, probably because of the disulfide bonds. Thus, structural alteration might be a valuable means of curtailing some of the various activities induced by the sarafotoxin/endothelin family of peptides.     

Functional endothelin/sarafotoxin receptors in the rat uterus

Functional receptors for the peptides of the endothelin (ET) and sarafotoxin (SRTX) families were detected in the rat uterus. These receptors specifically bind 125I-SRTX-b (Bmax = 220 fmol/mg protein), as well as ET-1, ET-3 and SRTX-c (IC50's 10, 5, 300 and 780 nM, respectively). Activation of the uterine ET/SRTX receptors induced dose-dependent phosphoinositide (PI) hydrolysis and three typical contractile responses: 1) increase in the muscle tonic tension; 2) increase in frequency of the spontaneous rhythmic contractions; 3) decrease of relaxation in each spontaneous rhythmic cycle. All three effects appeared at doses as low as 0.5-1 nM. Dose responses yield ED50 values of 5.5, 30 and 680 nM for ET-1, SRTX-b and ET-3, respectively. SRTX-c was the least effective peptide in achieving decrease in relaxation. In view of these results, and since the uterine responses to the peptides were almost immediate and reversible, we suggest that the functional ET/SRTX receptor of the rat uterus that is coupled to PI hydrolysis may be of physiological significance.     

Characterization of the central region containing the X-inactivation center and terminal region of the mouse X Chromosome using irradiation and fusion gene transfer hybrids

The irradiation and fusion gene transfer (IFGT) procedure provides a means of isolating subchromosomal fragments for use in the mapping of loci and for cloning probes from a particular area of a chromosome. Using this procedure, two large panels of somatic cell hybrids that contain mouse X Chromosome (Chr) fragments have been generated. These hybrid panels were generated by irradiating the monochromosomal mouse-hamster hybrid HYBX, which retains the mouse X Chr, with either 10 K or 50 K rads of X-irradiation followed by fusion with a recipient Chinese hamster cell line. IFGT hybrids retaining mouse material were generated at high frequency. These hybrids were used to orient loci in the X-inactivation center region that had not been resolvable in our interspecies backcross panel and also to map, within the terminal region of the X Chr, repeat elements detected by the probe p15-4. These hybrids not only complement existing interspecies meiotic mapping panels for the detailed analysis of specific regions of particular chromosomes, but also provide a potential source of material for chromosome-specific probe isolation.     

Genetic and molecular evidence of an X-chromosome deletion spanning the tabby (Ta) and testicular feminization (Tfm) loci in the mouse

A new radiation-induced mutation in the mouse, tabby-25H (Ta25H), has proved to be a deletion which spans both the tabby and testicular feminization (Tfm) loci on the X chromosome. The Ta phenotype closely resembles that of the original TaFa mutation in both the heterozygous and hemizygous conditions but Ta25H/Y animals additionally show the Tfm/Y phenotype, being externally female but possessing abdominally located testes. There is a shortage of both Ta25H/+ and Ta25H/Y classes relative to their normal sibs among the progeny of Ta25H/+ females at weaning age and this was indicated to be due to prenatal or neonatal losses. Exencephaly was observed in some members of both classes prior to birth. Both Ta25H classes tend to be runted at weaning but, remarkably, Ta25H/+ females often show a range of abnormalities not evident in Ta25H/Y animals. When probes for the Zfx, Ccg-1, Phk, and DXPas19 loci, which lie close to Ta, were hybridised to DNAs from Ta25H hemizygotes, the profiles of the X-linked bands were similar to those of control DNAs, suggesting these loci lie outside the deletion. However, a clear absence of an X-linked band was found with human androgen receptor probes, indicating that the Tfm locus is indeed missing. The deletion, therefore, extends a minimum of 1.5 cM and, with its proximal and distal boundaries partially defined, it could be as large as 4 cM. As Ta25H/+ females show the striped X-inactivation coat pattern, the putative X-inactivation centre, Xce, which lies close to Ta, cannot be located within the region deleted. The greasy (Gs) locus similarly appears to lie outside the deletion.     

Uridine diphosphate D-glucose dehydrogenase of Aerobacter aerogenes

Uridine diphosphate d-glucose dehydrogenase (EC 1.1.1.22) from Aerobacter aerogenes has been partially purified and its properties have been investigated. The molecular weight of the enzyme is between 70,000 and 100,000. Uridine diphosphate d-glucose is a substrate; the diphosphoglucose derivatives of adenosine, cytidine, guanosine, and thymidine are not substrates. Nicotinamide adenine dinucleotide (NAD), but not nicotinamide adenine dinucleotide phosphate, is active as hydrogen acceptor. The pH optimum is between 9.4 and 9.7; the K(m) is 0.6 mm for uridine diphosphate d-glucose and 0.06 mm for NAD. Inhibition of the enzyme by uridine diphosphate d-xylose is noncooperative and of mixed type; the K(i) is 0.08 mm. Thus, uridine diphosphate d-glucose dehydrogenase from A. aerogenes differs from the enzyme from mammalian liver, higher plants, and Cryptococcus laurentii, in which uridine diphosphate d-xylose functions as a cooperative, allosteric feedback inhibitor.     

Mapping of Murine Fibroblast Growth Factor Receptors Refines Regions of Homology between Mouse and Human Chromosomes

The genes for the fibroblast growth factor receptors Fgfr2, Fgfr3, and Fgfr4 have been mapped in the mouse using an interspecific backcross mapping panel. The Fgfr loci map to previously defined regions of homology between human and mouse chromosomes and provide additional information regarding human/mouse comparative mapping.