Several homologous connective tissue matrix degrading metalloproteinases, termed matrix metalloproteinase(MMPs), are secreted by resident tissue cells, infiltrating inflammatory cells, and tumor cells as inactive proenzymes that, upon activation, can degrade many of the connective tissue components. cDNA sequence analysis has revealed that these proteinases are composed of several modules, some of which appear to have been derived from matrix proteins. A family of specific tissue inhibitors of MMP(TIMPs) regulates the extracellular activity of MMPs. MMPs and TIMPs are differentially regulated in cells by growth factors, hormones and cell shape changes. Recent work has shown that lectins also stimulate MMP expression and suppresses TIMP levels in human fibroblasts indicating that naturally present lectins may also participate in regulating MW and TIMP gene expression in vivo.
A highly repetitive Mr=6.3×103 acidic glycan(G-6) of proteoglycan-like molecule mediates cell recognition and adhesion in the marine sponge Microciona prolifera. Specificity and sufficient adhesion strength is achieved through multiple binding of low affinity G-6 glycans to the cell surface receptors. This molecular mechanism is conceptually different from monovalent or tetravalent higher affinity interactions of adhesion and recognition molecules of immunoglobulin, cadherin, integrin and lectin families. The G-6 glycan is N-linked and contains glucuronic acid, fucose, mannose, galactose, N-acetyl glucosamine and sulfate. Such a unique composition indicates a novel type of structure with some features of glycosaminoglycans and N-linked polysaccharides.
Bindin is a 24kD protein, contained within the acrosomal granule of the sea urchin sperm, which is secreted upon contact of the sperm with the egg surface and mediates the species-specific attachment of sperm to the vitelline envelope. Early studies indicated that the egg surface receptor for bindin is a glycoprotein that contains sulfated fucan polysaccharide chains. Sulfated fucans isolated from the egg surface or from algal sources bind to bindin with moderately high affinity(Kd 5 x 10-9M) and inhibit the agglutination of eggs by bindin in vitro. Other naturally occurring sulfated polysaccharides (heparin, chondroitin sulfate, carrageenan) do not bind to bindin or inhibit bindin-mediated egg agglutination leading to the suggestion that bindin is a lectin-like protein specific for α 1, 2-fucose polysaccharides. More recent studies indicate that bindin is not a traditional lectin, but instead specifically recognizes sulfate esters on the polysaccharide backbone. The selectivity of bindin for sulfated fucans is apparently due to the complementary location of the sulfate esters on the fucan polysaccharide backbone. The species specific properties of the egg surface receptor for bindin are believed to reside in the core protein sequence of vitelline envelope glycoconjugates.
Embryogenesis requires the presice movement and reorganization of many cell types. Surface receptors provide the means with which cells make contact with the extracellular environment, and in so doing initiate differentiative events by transducing signals across the plasma membrane. Cell surface β1, 4 galactosyltransferase (GalTase) serves as a receptor during a variety of cellular interactions including fertilization, early embryonic cell-cell interactions, and cell interactions with the extracellular matrix. Surface GalTase functions during cell migration by binding to N-linked oligosaccharides on the E8 fragment of laminin. In vivo, surface GalTase participates in neural crest cell migration and neurulation, presumably by interacting with the laminin component of the basal lamina. Furthermore, surface GalTase functions during early mammalian embryogenesis by mediating cell-cell interactions of the compacting morula and the trophoblast stem cells of the ectoplacental cone. Immunological and molecular probes are being used to alter cell surface GalTase function in vitro and in vivo, in order to further define the precise role surface GalTase plays in embryonic morphogenesis.
Application of β-fructofuranosidase from Arthrobacter sp. K-1 to production of “functional oligosaccharides” including xylsucrose, isomaltosucrose and lactosucrose, and fructosylstevioside via transfructosylation was described. Xylsucrose and isomaltosucrose are non-cariogenic saccharides. Lactosucrose is non-digestive and has strong bifidus growth activity. The fructofuranosidase selectively transfers a fructosyl residue to the glucosyl residue at the 19-carboxyl group of stevioside. The quality of taste, bitterness, aftertaste and deliciousness of fructosylstevioside were greatly improved over those of stevioside.