The barrier function of skin: how to keep a tight lid on water loss

Without an epidermis, we would be in a sorry state. The epidermal layer not only protects us from environmental pathogens but also acts as a 'barrier' to water loss. The identification of the molecular nature of the barrier has occupied the efforts of skin researchers over many years, with the consensus in the field being that a protein-lipid layer, located in the upper layers of the epidermis, is necessary for establishment and maintenance of a water barrier. Now, evidence has been presented that components of intercellular junctions, termed tight junctions, also play an essential role in development of barrier function in the skin. Remarkably, the data support a hypothesis that was presented more than 30 years ago.     

Structural and thermodynamic characterization of the DNA binding properties of a triple alanine mutant of MATalpha2

Triply mutated MATalpha2 protein, alpha2-3A, in which all three major groove-contacting residues are mutated to alanine, is defective in binding DNA alone or in complex with Mcm1 yet binds with MATa1 with near wild-type affinity and specificity. To gain insight into this unexpected behavior, we determined the crystal structure of the a1/alpha2-3A/DNA complex. The structure shows that the triple mutation causes a collapse of the alpha2-3A/DNA interface that results in a reorganized set of alpha2-3A/DNA contacts, thereby enabling the mutant protein to recognize the wild-type DNA sequence. Isothermal titration calorimetry measurements reveal that a much more favorable entropic component stabilizes the a1/alpha2-3A/DNA complex than the alpha2-3A/DNA complex. The combined structural and thermodynamic studies provide an explanation of how partner proteins influence the sequence specificity of a DNA binding protein.     

Designing a 20-residue protein

Truncation and mutation of a poorly folded 39-residue peptide has produced 20-residue constructs that are >95% folded in water at physiological pH. These constructs optimize a novel fold, designated as the 'Trp-cage' motif, and are significantly more stable than any other miniprotein reported to date. Folding is cooperative and hydrophobically driven by the encapsulation of a Trp side chain in a sheath of Pro rings. As the smallest protein-like construct, Trp-cage miniproteins should provide a testing ground for both experimental studies and computational simulations of protein folding and unfolding pathways. Pro Trp interactions may be a particularly effective strategy for the a priori design of self-folding peptides.     

The Chediak-Higashi protein interacts with SNARE complex and signal transduction proteins

BACKGROUND:Chediak-Higashi syndrome (CHS) is an inherited immunodeficiency disease characterized by giant lysosomes and impaired leukocyte degranulation. CHS results from mutations in the lysosomal trafficking regulator (LYST) gene, which encodes a 425-kD cytoplasmic protein of unknown function. The goal of this study was to identify proteins that interact with LYST as a first step in understanding how LYST modulates lysosomal exocytosis. MATERIALS AND METHODS: Fourteen cDNA fragments, covering the entire coding domain of LYST, were used as baits to screen five human cDNA libraries by a yeast two-hybrid method, modified to allow screening in the activation and the binding domain, three selectable markers, and more stringent confirmation procedures. Five of the interactions were confirmed by an in vitro binding assay. RESULTS: Twenty-one proteins that interact with LYST were identified in yeast two-hybrid screens. Four interactions, confirmed directly, were with proteins important in vesicular transport and signal transduction (the SNARE-complex protein HRS, 14-3-3, and casein kinase II). CONCLUSIONS:On the basis of protein interactions, LYST appears to function as an adapter protein that may juxtapose proteins that mediate intracellular membrane fusion reactions. The pathologic manifestations observed in CHS patients and in mice with the homologous mutation beige suggest that understanding the role of LYST may be relevant to the treatment of not only CHS but also of diseases such as asthma, urticaria, and lupus, as well as to the molecular dissection of the CHS-associated cancer predisposition.     

An european pupil project linked to the scientific aims of the experiment AQUARIUS-XENOPUS on the taxi Soyuz flight Andromede to ISS

The German-French biological experiment AQUARIUS-XENOPUS which flew on the Soyuz flight Andromede to the International Space Station ISS (launched October 21, 2001 in Baikonour/Kazakhstan) was extended by an outreach project. Pupils of class 10 to 12 from Ulm/D and Nancy-Tomblaine/F studied swimming behavior of Xenopus tadpoles on ground. They were instructed to perform all experimental steps following the protocol of similar video recordings on ISS. After the flight, they evaluated the kinetics of swimming of both ground controls and space animals. The pupil project included theoretical components to introduce them to the field of gravitational biology. One feature of the project was the exchange of ideas between pupils by meetings which took place in Ulm (June 2001), Nancy (February 2002) and Paris (May 2002). We consider our approach as a successful way to include young people in space experiments on a cheap cost level and to bring ideas of gravitational biology into the curricula of European schools.     

Physical mapping of genes in somatic cell radiation hybrids by comparative genomic hybridization to cDNA microarrays

Background  

Somatic cell mutants can be informative in the analysis of a wide variety of cellular processes. The use of map-based positional cloning strategies in somatic cell hybrids to analyze genes responsible for recessive mutant phenotypes is often tedious, however, and remains a major obstacle in somatic cell genetics. To fulfill the need for more efficient gene mapping in somatic cell mutants, we have developed a new DNA microarray comparative genomic hybridization (array-CGH) method that can rapidly and efficiently map the physical location of genes complementing somatic cell mutants to a small candidate genomic region. Here we report experiments that establish the validity and efficacy of the methodology.     

Tiny telomere DNA

We describe the design, synthesis and biophysical characterization of a novel DNA construct in which a folded quadruplex structure is joined to a standard double helix. Circular dichroism, gel electrophoresis, three-dimensional UV melting and differential scanning calorimetry were all used to characterize the structure. Rigorous molecular dynamics simulations were used to build a plausible atomic-level structural model of the DNA construct. This novel DNA construct provides a model for the duplex–quadruplex junction region at the end of chromosomal DNA and offers a system for the study of structure-selective ligand binding.     

Estimation of single nucleotide polymorphism allele frequency in DNA pools by using Pyrosequencing

Positional cloning of genes underlying complex diseases, such as type 2 diabetes mellitus (T2DM), typically follows a two-tiered process in which a chromosomal region is first identified by genome-wide linkage scanning, followed by association analyses using densely spaced single nucleotide polymorphic markers to identify the causal variant(s). The success of genome-wide single nucleotide polymorphism (SNP) detection has resulted in a vast number of potential markers available for use in the construction of such dense SNP maps. However, the cost of genotyping large numbers of SNPs in appropriately sized samples is nearly prohibitive. We have explored pooled DNA genotyping as a means of identifying differences in allele frequency between pools of individuals with T2DM and unaffected controls by using Pyrosequencing technology. We found that allele frequencies in pooled DNA were strongly correlated with those in individuals (r=0.99, P<0.0001) across a wide range of allele frequencies (0.02-0.50). We further investigated the sensitivity of this method to detect allele frequency differences between contrived pools, also over a wide range of allele frequencies. We found that Pyrosequencing was able to detect an allele frequency difference of less than 2% between pools, indicating that this method may be sensitive enough for use in association studies involving complex diseases where a small difference in allele frequency between cases and controls is expected.