The molecular basis of color vision in colorful fish: Four Long Wave-Sensitive (LWS) opsins in guppies (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>) are defined by amino acid substitutions at key functional sites

Background  

Comparisons of functionally important changes at the molecular level in model systems have identified key adaptations driving isolation and speciation. In cichlids, for example, long wavelength-sensitive (LWS) opsins appear to play a role in mate choice and male color variation within and among species. To test the hypothesis that the evolution of elaborate coloration in male guppies (Poecilia reticulata) is also associated with opsin gene diversity, we sequenced long wavelength-sensitive (LWS) opsin genes in six species of the family Poeciliidae.     

Crystal structure of the CheA histidine phosphotransfer domain that mediates response regulator phosphorylation in bacterial chemotaxis

The x-ray crystal structure of the P1 or H domain of the Salmonella CheA protein has been solved at 2.1-A resolution. The structure is composed of an up-down up-down four-helix bundle that is typical of histidine phosphotransfer or HPt domains such as Escherichia coli ArcB(C) and Saccharomyces cerevisiae Ypd1. Loop regions and additional structural features distinguish all three proteins. The CheA domain has an additional C-terminal helix that lies over the surface formed by the C and D helices. The phosphoaccepting His-48 is located at a solvent-exposed position in the middle of the B helix where it is surrounded by several residues that are characteristic of other HPt domains. Mutagenesis studies indicate that conserved glutamate and lysine residues that are part of a hydrogen-bond network with His-48 are essential for the ATP-dependent phosphorylation reaction but not for the phosphotransfer reaction with CheY. These results suggest that the CheA-P1 domain may serve as a good model for understanding the general function of HPt domains in complex two-component phosphorelay systems.     

High frequency hearing loss correlated with mutations in the GJB2 gene

Genetic hearing impairment affects approximately 1/2000 live births. Mutations in one gene, GJB2, coding for connexin 26 cause 10%-20% of all genetic sensorineural hearing loss. Mutation analysis in the GJB2 gene and audiology were performed on 106 families presenting with at least one child with congenital hearing loss. The families were recruited from a hospital-based multidisciplinary clinic, which functions to investigate the aetiology of sensorineural hearing loss in children and which serves an ethnically diverse population. In 74 families (80 children), the aetiology was consistent with non-syndromic recessive hearing loss. Six different connexin 26 mutations, including one novel mutation, were identified. We show that GJB2 mutations cause a range of phenotypes from mild to profound hearing impairment and that loss of hearing in the high frequency range (4000-8000 Hz) is a characteristic feature in children with molecularly diagnosed connexin 26 hearing impairment. We also demonstrate that this type of audiology and high frequency hearing loss is found in a similar-sized group of deaf children in whom a mutation could only be found in one of the connexin 26 alleles, suggesting connexin 26 involvement in the aetiology of hearing loss in these cases. In our study of the M34T mutation, only compound heterozygotes exhibited hearing loss, suggesting autosomal recessive inheritance.     

Crystal structure of leucotoxin S component: new insight into the Staphylococcal beta-barrel pore-forming toxins

Staphylococcal leucocidins and gamma-hemolysins (leucotoxins) are bi-component toxins that form lytic transmembrane pores. Their cytotoxic activities require the synergistic association of a class S component and a class F component, produced as water-soluble monomers that form hetero-oligomeric membrane-associated complexes. Strains that produce the Panton-Valentine leucocidin are clinically associated with cutaneous lesions and community-acquired pneumonia. In a previous study, we determined the crystal structure of the F monomer from the Panton-Valentine leucocidin. To derive information on the second component of the leucotoxins, the x-ray structure of the S protein from the Panton-Valentine leucocidin was solved to 2.0 angstrom resolution using a tetragonal crystal form that contains eight molecules in the asymmetric unit. The structure demonstrates the different conformation of the domain involved in membrane contacts and illustrates sequence and tertiary structure variabilities of the pore-forming leucotoxins. Mutagenesis studies at a key surface residue (Thr-28) further support the important role played by these microheterogeneities for the assembly of the bipartite leucotoxins.     

Tyrosine phosphorylation of myosin heavy chain during skeletal muscle differentiation: an integrated bioinformatics approach

Previously it has been shown that insulin-mediated tyrosine phosphorylation of myosin heavy chain is concomitant with enhanced association of C-terminal SRC kinase during skeletal muscle differentiation. We sought to identify putative site(s) for this phosphorylation event. A combined bioinformatics approach of motif prediction and evolutionary and structural analyses identified tyrosines163 and 1856 of the skeletal muscle heavy chain as the leading candidate for the sites of insulin-mediated tyrosine phosphorylation. Our work is suggestive that tyrosine phosphorylation of myosin heavy chain, whether in skeletal muscle or in platelets, is a significant event that may initiate cytoskeletal reorganization of muscle cells and platelets. Our studies provide a good starting point for further functional analysis of MHC phosphor-signalling events within different cells.     

Scale-up issues for in situ anaerobic tetrachloroethene bioremediation

For the full scale implementation of in situ anaerobic bioremediation of tetrachloroethene (PCE) in groundwater, the following issues must be addressed: which organic substrates at which concentration would be most effective in promoting dechlorination and are economical; how far the substrate, electron acceptor, and nutrients can be transported in the aquifer; and the placement of delivery and recovery wells for distributing these amendments. In a microcosm study, almost all of the tested inexpensive substrates supported reductive dechlorination of PCE through vinyl chloride (VC) under methanogenic conditions. A minimum of about 60 mg L⁻¹ of organic carbon was needed to dechlorinate 23 μM PCE with a single feeding. In a second microcosm study dechlorination stopped at 1,2-dichloroethene (DCE) in microcosms fed higher concentrations of several substrates. At the highest concentrations the substrates inhibited DCE production. Three field tracer tests were conducted to evaluate methods to distribute the amendments across the aquifer. The natural groundwater gradient is not sufficient to distribute substrate evenly. Groundwater injection at 60 times the natural flux rate increased the distribution of substrate. A mixing strategy of cross-gradient injection further increased the distribution of the substrate. Ammonia-nitrogen, sulfate, and phosphate were retarded relative to the substrate and inorganic tracer. Received 30 October 1995/ Accepted in revised form 07 June 1996     

Association between chloroplast and mitochondrial lineages in oaks

Patterns of chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) variation were studied in 378 populations of oak trees sampled throughout the southern half of France. Six cpDNA haplotypes detected in a previous European survey and three new cpDNA haplotypes were found in this region. Two mitochondrial polymorphisms detected earlier by restriction analysis of PCR-amplified fragments alone, or in combination with single-strand conformation polymorphism (SSCP), were compared with the cpDNA data. Sequencing revealed the nature of the two mitochondrial mutations: a single-base substitution and a 4-bp inversion associated with a 22-bp hairpin secondary structure. The single-base substitution was then analyzed by allele-specific amplification. Results for the two cytoplasmic genomes were combined, which allowed the identification of 12 cpDNA-mtDNA haplotypes. The 4-bp mtDNA inversion has appeared independently in different cpDNA lineages. Given the peculiar nature of this mtDNA mutation, we suggest that intramolecular recombination leading to repeated inversions of the 4-bp sequence (rather than paternal leakage of one of the two genomes) is responsible for this pattern. Furthermore, the geographic locations of the unusual cpDNA-mtDNA associations (due to the inversion) usually do not match the zones of contact between divergent haplotypes. In addition, in southern France, the groupings of populations based on the mtDNA substitution were strictly congruent with those based on cpDNA. Because many populations that are polymorphic for both cpDNA and mtDNA have remained in contact since postglacial recolonization in this area without producing any new combination of cytoplasms involving the mitochondrial substitution, we conclude that paternal leakage is not a significant factor at this timescale. Such results confirm and expand our earlier conclusions based on controlled crosses.