Chemical derivatization of therapeutic proteins

Poly(Ethylene Glycol)-Bovine Serum Albumin Hydrogel as a Matrix for Enzyme Immobilization. In Vitro Biochemical Characterization

Arginase, isolated from beef liver, apyrase and glutaminase, isolated from Escherichia coli, were immobilized during the synthesis of a hydrogel matrix made from poly(ethylene glycol) (PEG) and bovine serum albumin (BSA). After synthesis, a one- to three-fold increase in the K m values was observed for the enzymes. The apparent K m were 30 mM of arginine, 6.5 mM of glutamine, and 52 μM of ATP for immobilized arginase, glutaminase, and apyrase, respectively. In general, immobilization allowed the enzymes to retain most of their initial activity; after incubating for 1 month at 37°C in the presence of the respective substrates, more than 95% of the initial activity was found. The optimal temperatures varied from 40 to 60°C for all enzyme preparations. The immobilized arginase, glutaminase, and apyrase had optimal activity over a larger pH range which was due to the matrix effect. Surface modification of arginase with 5,000 Mw methoxy-PEG increased the stability for up to 24 days (incubated at 37°C) compared to eight days for the native enzyme tested under the same conditions. However, this modification did not affect the stability of glutaminase.

Electron Capture Dissociation Mass Spectrometry in Characterization of Peptides and Proteins

Electron capture dissociation (ECD) represents one of the most recent and significant advancements in tandem mass spectrometry (MS/MS) for the identification and characterization of polypeptides. In comparison with the conventional fragmentation techniques, such as collisionally activated dissociation (CAD), ECD provides more extensive sequence fragments, while allowing the labile modifications to remain intact during backbone fragmentation--an important attribute for characterizing post-translational modifications. Herein, we present a brief overview of the ECD technique as well as selected applications in characterization of peptides and proteins. Case studies including characterization and localization of amino acid glycosylation, methionine oxidation, acylation, and "top-down" protein mass spectrometry using ECD will be presented. A recent technique, coined as electron transfer dissociation (ETD), will be also discussed briefly.

Effects of chemical modifiers on recombinant factor VIII activity

Factor VIII performs a critical role in the blood coagulation cascade but is extremely labile. We have carried out chemical studies on a fully functional recombinant Factor VIII (rFVIII) using a variety of protein modifying agents, some of which were bifunctional. Thiol-specific maleimides cause no activity loss despite a substantial decrease in rFVIII's free thiol content. Mild oxidation procedures had either neutral or adverse effects on activity. Amino-specific reagents led to significant losses of rFVIII procoagulant activity. It appears that free amino groups are essential for Factor VIII's function while some at least of its many free thiol groups are not. None of these derivatives was any less labile than unmodified rFVIII. Systematic chemical modification of important proteins in this way can give useful insights into appropriate protein engineering strategies.

Understanding and increasing protein stability

This review surveys the processes leading to loss of protein function and the types of molecular interaction that help stabilize proteins. It considers the effects of organic solvents on stability and the special features of thermophilic proteins. The deliberate manipulation of stability by protein engineering is discussed using the enzyme subtilisin as example. Both random and rational mutations of this protein have led to variants with greatly improved tolerances of high temperatures and organic solvents. One can also use chemical modification to modify protein stability and some of the main approaches are reviewed. The chemical and genetic strategies are complementary and have been combined to stabilize cytochrome c by metal-mediated cross-linking following site-specific mutagenesis. The article concludes by summarizing the beneficial effects of certain additives on protein stability.