The Molecular Physiology of Electroneutral Cation-Chloride Cotransport

The application of molecular biology to the study of electroneutral cation-chloride cotransporters has been extremely successful, resulting in the identification of a new gene family of five membrane proteins. The function, expression, and regulation of these important proteins can increasingly be described in molecular terms. In addition, mutations in two renal cation-chloride transporter genes have been found in patients with Bartter's and Gitelman's syndromes, autosomal recessive disorders of renal salt excretion. Received: 14 February 1997     

Crystallization patterns of membrane-bound (Na+ +K+)-ATPase

Extensive formation of two-dimensional crystals of the proteins of the pure membrane-bound (Na+ +K+)-ATPase is induced during prolonged incubation with vanadate and magnesium. Some membrane crystals are formed in medium containing magnesium and phosphate. Computer-averaged images of the two-dimensional crystals show that the unit cell in vanadate-induced crystals contains a protomeric alpha beta-unit of the enzyme protein. In phosphate-induced crystals an (alpha beta) 2-unit occupies one unit cell suggesting the interactions between alpha beta-units can be of importance in the function of the Na+, K+ pump.     

Protein folding and maturation in a cell-free system.

Reduced cellular systems have provided important tools to study complex cellular processes. Here we describe the oxidation, oligomerization, and chaperone binding of the viral glycoprotein influenza hemagglutinin in a cell-free system. The cell-free system, comprised of rough endoplasmic reticulum derived microsomes and a reticulocyte lysate, supported the complete maturation of hemagglutinin from the earliest oxidative intermediate to the mature homo-oligomer. Hemagglutinin disulfide bond formation and oligomerization were found to occur in a time- and temperature-dependent manner. Hemagglutinin's temporal association with the molecular chaperones calnexin and calreticulin was similar to that observed for their association with elongating ribosome-attached nascent chains in live cells. Furthermore, a procedure is described that permits the translocation of protein into microsomes that are depleted of lumenal contents. This cell-free system, therefore, provided an effective means to study the biological maturation processes of a protein that traverses the secretory pathway.     

The three-dimensional structure of trypsin-treated Staphylococcus aureus α-toxin

Trypsin treatment of staphylococcal α-toxin cleaves the molecule into two roughly equally sized parts, which ] results in inactivation of the toxin. Tetragonal arrays of oligomers, closely resembling the native ones, can however be formed on lipid layers. From tilted views of negatively stained crystals a 31) structure to 23 Å resolution has been determined by electron microscopy and image processing. On comparison with the 31) structure of the native ot-toxin (Olofsson et al., J. Mol. Biol. 214, 299–306, 1990) the subdomains are more separated, confirming the differences found when comparing the projection maps (Olofsson et al., J. Struct. Biol. 106, 199–204, 1991). The tryptic cleavage takes place in a postulated hinge region. The results are consistent with the hypothesis that the conformational change required for inducing the membrane permeabilizing property takes place in this region. Furthermore, we present a refined projection map at approximately 10 Å resolution based on the analysis of a large number of crystals using unbending methods.     

bold: The Barcode of Life Data System (http://www.barcodinglife.org)

The Barcode of Life Data System (bold) is an informatics workbench aiding the acquisition, storage, analysis and publication of DNA barcode records. By assembling molecular, morphological and distributional data, it bridges a traditional bioinformatics chasm. bold is freely available to any researcher with interests in DNA barcoding. By providing specialized services, it aids the assembly of records that meet the standards needed to gain BARCODE designation in the global sequence databases. Because of its web-based delivery and flexible data security model, it is also well positioned to support projects that involve broad research alliances. This paper provides a brief introduction to the key elements of bold, discusses their functional capabilities, and concludes by examining computational resources and future prospects.     

DIFFERENCES IN POLYSACCHARIDE STRUCTURE BETWEEN CALCIFIED AND UNCALCIFIED SEGMENTS IN THE CORALLINE CALLIARTHRON CHEILOSPORIOIDES (CORALLINALES,RHODOPHYTA)1

The articulated coralline Calliarthron cheilosporioides Manza produces segmented fronds composed of calcified segments (intergenicula) separated by uncalcified joints (genicula), which allow fronds to bend and reorient under breaking waves in the wave‐swept intertidal zone. Genicula are formed when calcified cells decalcify and restructure to create flexible tissue. The present study has identified important differences in the main agaran disaccharidic repeating units [→3)‐β‐d ‐Galp (1→ 4)‐α‐l ‐Galp(1→] synthesized by genicular and intergenicular segments. Based on chemical and spectroscopical analyses, we report that genicular cells from C. cheilosporioides biosynthesize a highly methoxylated galactan at C‐6 position with low levels of branching with xylose side stubs on C‐6 of the [→3)‐β‐d ‐Galp (1→] units, whereas intergenicular segments produce xylogalactans with high levels of xylose and low levels of 6‐O‐methyl β‐d ‐Gal units. These data suggest that, during genicular development, xylosyl branched, 3‐linked β‐d ‐Galp units present in the xylogalactan backbones from intergenicular walls are mostly replaced by 6‐O‐methyl‐d‐ galactose units. We speculate that this structural shift is a consequence of a putative and specific methoxyl transferase that blocks the xylosylation on C‐6 of the 3‐linked β‐d ‐Galp units. Changes in galactan substitutions may contribute to the distinct mechanical properties of genicula and may lend insight into the calcification process in coralline algae.