Selective Hydrolysis of Transferrin Promoted by Zr-Substituted Polyoxometalates.

The hydrolysis of the iron-binding blood plasma glycoprotein transferrin (Tf) has been examined at pH = 7.4 in the presence of a series of Zr-substituted polyoxometalates (Zr-POMs) including Keggin (EtNH)[Zr(PWO)]∙7HO (), (EtNH)[{-PWOZr-(-OH) (HO)}]∙7HO (), Wells-Dawson KH[Zr(-PWO)]·25HO (), Na[Zr(-PWO)(-O)(-OH)(HO)]·57HO () and Lindqvist (MeN)[ZrWO(HO)] (), (nBuN)[(ZrWO(-OH))]∙2HO ()) type POMs. Incubation of transferrin with Zr-POMs resulted in formation of 13 polypeptide fragments that were observed on sodium dodecyl sulfate poly(acrylamide) gel electrophoresis (SDS-PAGE), but the hydrolysis efficiency varied depending on the nature of Zr-POMs.

Selective Hydrolysis of Terminal Glycosidic Bond in α-1-Acid Glycoprotein Promoted by Keggin and Wells-Dawson Type Heteropolyacids.

The reactivity of a range of Keggin and Wells-Dawson type heteropolyacids (HPAs): H PW O H SiW O , H PMo O , K P W O , and NaH W O , towards the heavily glycosylated α-1-acid glycoprotein (AGP) is reported. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) show that after incubation of the protein with HPAs at 80 °C and pH 2.8 complete hydrolysis of terminal glycosidic bond has been achieved, resulting in the removal of sialic acids with no observed destruction of the protein core or the residual glycan chains.

Interactions between polyoxometalates and biological systems: from drug design to artificial enzymes.

Polyoxometalates have long been studied in a variety of biological applications. Interactions between the highly charged POM molecules and biological molecules frequently occur through hydrogen-bonding and electrostatic interactions. Tellurium-centred Anderson-Evans POMs show exceptional promise as crystallization agents, while acidic and metal-substituted POMs may provide interesting alternatives to enzymes in proteomics applications.

Polyoxometalates as sialidase mimics: selective and non-destructive removal of sialic acid from a glycoprotein promoted by phosphotungstic acid.

The selective hydrolysis of the glycosidic bond between the terminal sialic acid and the penultimate sugar has been achieved in the alpha-2-HS-glycoprotein (Fetuin-A) in the presence of HPWO, a Keggin type polyoxometalate. A controlled liberation of sialic acid from the glycoprotein could be achieved at pH 3.0 and 37 °C without the destruction of the protein backbone.