Hydrazinolysis of heparin and other glycosaminoglycans.

Heparin, carboxy-group-reduced heparin, several sulphated monosaccharides and disaccharides formed from heparin, and a tetrasaccharide prepared from chondroitin sulphate were treated at 100 degrees C with hydrazine containing 1% hydrazine sulphate for periods sufficient to cause complete N-deacetylation of the N-acetylhexosamine residues. Under these hydrazinolysis conditions both the N-sulphate and the O-sulphate substituents on these compounds were completely stable. However, the uronic acid residues were converted into their hydrazide derivatives at rates that depended on the uronic acid structures. Unsubstituted L-iduronic acid residues reacted much more slowly than did unsubstituted D-glucuronic acid or 2-O-sulphated L-iduronic acid residues. The chemical modification of the carboxy groups resulted in a low rate of C-5 epimerization of the uronic acid residues. The hydrazinolysis reaction also caused a partial depolymerization of heparin but not of carboxy-group-reduced heparin. Treatment of the hydrazinolysis products with HNO2 at either pH 4 or pH 1.5 or with HIO3 converted the uronic acid hydrazides back into uronic acid residues. The use of the hydrazinolysis reaction in studies of the structures of uronic acid-containing polymers and the implications of the uronic acid hydrazide formation are discussed.     

Laminins and other strange proteins.

Laminins are large multidomain proteins of the extracellular matrix (ECM) with important functions in the development and maintenance of cellular organization and supramolecular structure, in particular in basement membranes. Each molecule is composed of three polypeptide chains, A (300-400 kDa) and B1 and B2 (180-200 kDa), which together form the characteristic cross-shaped laminin structure with three short arms and one long arm. Many different domains have been identified in laminin by sequence analysis, structural investigations, and functional studies. Each short arm is formed by homologous N-terminal portions of one of the three chains. Structurally, each short arm contains two or three globular domains which are connected by rows of manyfold-repeated Cys-rich "EGF-like" domains. In all three chains this region is followed by a long heptad repeat region similar to those found in many alpha-helical coiled-coil proteins. These parts of the three laminin chains constitute a triple-stranded coiled-coil domain, which forms the extended rodlike structure of the long arm. This is the only domain in the protein which is made up of more than one chain and consequently serves the function of chain assembly. The two B chains are terminated by the coiled-coil domain, but the A chain contains an additional C-terminal segment which accounts for five globular domains located at the tip of the long arm. Several important functions of laminin have been assigned to individual domains in either the short arms or terminal regions of the long arm.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transvection and other homology effects.

The presence of homologous nucleic acid sequences can exert profound effects on chromosomal and gene function in a wide range of organisms. These homology effects reveal remarkable forms of regulation as well as suggest possible avenues for the development of new technologies.     

Dimerization and other changes of aminoethylcysteine ketimine.

High performance liquid chromatography and gas liquid chromatography have been used for the study of the stability of aminoethylcysteine-ketimine (AECK) in different experimental conditions. Concentration and acidic pH lead to the formation of the dimer of AECK which is very sensitive to temperature and is slowly converted to the corresponding decarboxylated dimer even at room temperature. In the presence of air at neutral and alkaline pH AECK is converted to an unknown compound having spectral characteristics similar to AECK and to other compounds not detectable by HPLC. Under nitrogen at neutral pH AECK is more stable and only undergoes the dimerization reaction to some extent.     

Vaccinia and other poxvirus expression vectors.

Over the past year improvements have been made in recombinant vaccinia virus gene expression and a new method for inserting DNA into the poxvirus genome has been developed, along with alternative methods for selecting recombinant viruses. Attenuated and non-replicating vaccinia virus and avian poxvirus vectors are now being used successfully. Field trials of an oral, wild-life rabies vaccine and phase 1 testing of human vaccines derived from vaccinia virus are underway.     

Structure and interactions of desmosomal and other cadherins.

The cadherin superfamily of cell-cell adhesion molecules is now known to include proteins of the desmosome as well as of the adherens type of junction. The desmosomal cadherins consist of two families of proteins, the desmocollins and the desmogleins, both of which are represented by different isoforms which are differentially expressed in epidermis. The desmocollins are quite similar to the classic cadherins in overall structure, but with alternatively spliced variants; the desmogleins have extra cytoplasmic sequences added onto the basic cadherin structure. The cytoplasmic domains are specialized for binding to 'mediator' proteins, such as plakoglobin, which interconnect to the intermediate filament system rather than the actin filaments as do the classic cadherins.