Galactokinases: potential biotechnological applications as biocatalysts

Galactokinase, a member of the GHMP (galactokinase, homoserine kinase, mevalonate kinase, phosphomevalonate kinase) family of kinases, catalyses the ATP-dependent phosphorylation of galactose at position 1 on the sugar. This reaction is important in the Leloir pathway of galactose catabolism. The need to produce monosaccharides phosphorylated at position 1 for the synthesis of complex molecules, including aminoglycoside antibiotics, has stimulated interest in exploiting the catalytic potential of galactokinases. However, the enzyme is quite specific, generally only catalysing the phosphorylation of D-galactose and closely related molecules. Directed evolution strategies have identified a key tyrosine residue (Tyr-371 in the Escherichia coli enzyme) which, although distant from the active site, influences the specificity of the enzyme. Alteration of this residue to histidine in E. coli and Lactococcus lactis galactokinases dramatically expanded the substrate range to include both D- and L-sugars. Similar experiments with the human enzyme demonstrated that alteration of the equivalent tyrosine (Tyr-379) to cysteine, lysine, arginine, serine or tryptophan increased the catalytic promiscuity of the enzyme. It has been hypothesised that these specificity changes arise because of alterations in the flexibility of the polypeptide chain. This hypothesis has yet to be tested experimentally. The biotechnological potential of galactokinases is clearly considerable and exploitation of closely related enzymes such as N-acetylgalactosamine kinase and arabinose kinase would expand that potential still further.

Mechanisms of plant resistance to metal and metalloid ions and potential biotechnological applications

Metal and metalloid resistances in plant species and genotypes/accessions are becoming increasingly better understood at the molecular and physiological level. Much of the recent focus into metal resistances has been on hyperaccumulators as these are excellent systems to study resistances due to their very abnormal metal(loid) physiology and because of their biotechnological potential. Advances into the mechanistic basis of metal(loid) resistances have been made through the investigation of metal(loid) transporters, the construction of mutants with altered metal(loid) transport and metabolism, a better understanding of the genetic basis of resistance and hyperaccumulation and investigations into the role of metal(loid) ion chelators. This review highlights these recent advances. © Springer 2005.

A Review on Bradykinin-Related Peptides Isolated from Amphibian Skin Secretion

Amphibian skin secretion has great potential for drug discovery and contributes hundreds of bioactive peptides including bradykinin-related peptides (BRPs). More than 50 BRPs have been reported in the last two decades arising from the skin secretion of amphibian species. They belong to the families Ascaphidae (1 species), Bombinatoridae (3 species), Hylidae (9 speices) and Ranidae (25 species). This paper presents the diversity of structural characteristics of BRPs with N-terminal, C-terminal extension and amino acid substitution. The further comparison of cDNA-encoded prepropeptides between the different species and families demonstrated that there are various forms of kininogen precursors to release BRPs and they constitute important evidence in amphibian evolution. The pharmacological activities of isolated BRPs exhibited unclear structure–function relationships, and therefore the scope for drug discovery and development is limited. However, their diversity shows new insights into biotechnological applications and, as a result, comprehensive and systematic studies of the physiological and pharmacological activities of BRPs from amphibian skin secretion are needed in the future.