Cyclopentadiene as a Multifunctional Reagent for Normal- and Inverse-Electron Demand Diels-Alder Bioconjugation.

Optimizing the Diels-Alder (DA) reaction for aqueous coupling has resulted in practical methods to link molecules such as drugs and diagnostic agents to proteins. Both normal electron demand (NED) and inverse electron demand (IED) DA coupling schemes have been employed, but neither mechanism entails a common multipurpose reactive group. This report focuses on expanding the bioconjugation toolbox for cyclopentadiene through the identification of reactive groups that couple through NED or IED mechanisms in aqueous solution. Dienophiles and tetrazine derivatives were screened for reactivity and selectivity toward antibodies bearing cyclopentadiene amino acids to yield bioconjugates. Twelve NED dienophiles and four tetrazine-based IED substrates were identified as capable of practical biocoupling. Furthermore, tetrazine ligation to cyclopentadiene occurred at a rate of 3.3 ± 0.5 M-1 s-1 and was capable of bioorthogonal transformations, as evidenced by the selective protein labeling in serum. Finally, an antibody-drug conjugate (ADC)-bearing monomethyl auristatin E was prepared via tetrazine conjugation to cyclopentadiene. The resulting ADC was stable and demonstrated potent activity in vitro. These findings expand the utility of cyclopentadiene as a tool to couple entities to proteins via dual DA addition mechanisms.

A Reactive Antibody Platform for One-Step Production of Antibody-Drug Conjugates through a Diels-Alder Reaction with Maleimide.

The normal electron-demand Diels-Alder (DA) cycloaddition is a classic transformation routinely used in synthesis; however, applications in biological systems are limited. Here, we report a spiro[2.4]hepta-4,6-diene-containing noncanonical amino acid (SCpHK) capable of efficient incorporation into antibodies and subsequent coupling with maleimide via a DA reaction. SCpHK was stable throughout protein expression in mammalian cells and enabled covalent attachment of maleimide drug-linkers yielding DA antibody-drug conjugates (DA-ADCs) with nearly quantitative conversion in a one-step process. The uncatalyzed DA reaction between SCpHK and maleimide in aqueous buffer was rapid (1.8-5.4 M-1 s-1), and the antibody-drug adduct was stable in rat serum for at least 1 week at 37 °C. Anti-EphA2 DA-ADCs containing AZ1508 or SG3249 maleimide drug-linkers were potent inhibitors of tumor growth in PC3 tumor models in vivo. The DA bioconjugation strategy described here represents a simple method to produce site-specific and stable ADCs with maleimide drug-linkers.

Thermal Stabilization of Erwinia chrysanthemi pectin methylesterase a for application in a sugar beet pulp biorefinery.

Directed evolution approaches were used to construct a thermally stabilized variant of Erwinia chrysanthemi pectin methylesterase A. The final evolved enzyme has four amino acid substitutions that together confer a T(m) value that is approximately 11 degrees C greater than that of the wild-type enzyme, while maintaining near-wild-type kinetic properties. The specific activity, with saturating substrate, of the thermally stabilized enzyme is greater than that of the wild-type enzyme when both are operating at their respective optimal temperatures, 60 degrees C and 50 degrees C. The engineered enzyme may be useful for saccharification of biomass, such as sugar beet pulp, with relatively high pectin content. In particular, the engineered enzyme is able to function in biomass up to temperatures of 65 degrees C without significant loss of activity. Specifically, the thermally stabilized enzyme facilitates the saccharification of sugar beet pulp by the commercial pectinase preparation Pectinex Ultra SPL. Added pectin methylesterase increases the initial rate of sugar production by approximately 50%.

Gateway cloning for protein expression.

The rate-limiting step in protein production is usually the generation of an expression clone that is capable of producing the protein of interest in soluble form at high levels. Although cloning of genes for protein expression has been possible for some time, efficient generation of functional expression clones, particularly for human proteins, remains a serious bottleneck. Often, such proteins are hard to produce in heterologous systems because they fail to express, are expressed as insoluble aggregates, or cannot be purified by standard methods. In many cases, researchers are forced to return to the cloning stages to make a new construct with a different purification tag, or perhaps to express the protein in a different host altogether. This usually requires identifying new cloning schemes to move a gene from one vector to another, and frequently requires multistep, inefficient cloning processes, as well as lengthy verification and sequence analysis. Thus, most researchers view this as a linear pathway - make an expression clone, try it out, and if it fails, go back to the beginning and start over. Because of this, protein expression pipelines can be extremely expensive and time consuming.The advent of recombinational cloning has dramatically changed the way protein expression can be handled. Rapid production of parallel expression clones is now possible at relatively low cost, opening up many possibilities for both low- and high-throughput protein expression, and increasing the flexibility of expression systems that researchers have available to them. While many different recombinational cloning systems are available, the one with the highest level of flexibility remains the Gateway system. Gateway cloning is rapid, robust, and highly amenable to high-throughput parallel generation of expression clones for protein production.

Improved recombinational stability of lentiviral expression vectors using reduced-genome Escherichia coli.

Lentiviral expression clones, which contain long direct repeats, often show dramatic instability in Escherichia coli, leading to difficulties in obtaining valid clones. We show that the reduced-genome E. coli strain MDS42 is capable of stabilizing lentiviral expression clones containing direct repeats, and outperforms many commonly used cloning strains for this purpose. In addition, the strain has several characteristics that make it highly amenable for use in recombinational cloning systems.