Expression and tandem affinity purification of 20S proteasomes and other multisubunit complexes in Haloferax volcanii

Tandem affinity purification is a useful strategy to isolate multisubunit complexes of high yield and purity but can be limited when working with halophilic proteins that are not properly expressed in Escherichia coli. Halophilic proteins are desirable for bioindustrial applications as they are often stable and active in organic solvents; however, these proteins can be difficult to express, fold, and purify by traditional technologies. Haloarchaea provide a useful alternative for expression of halophilic proteins. These microorganisms use a salt-in strategy to maintain homeostasis and express most of their proteins with halophilic properties and low pI. Here, we provide detailed protocols for the genetic modification, expression and tandem affinity purification of "salt-loving" multisubunit complexes from the haloarchaeon Haloferax volcanii. The strategy for isolation of affinity tagged 20S proteasomes that form cylindrical proteolytic nanomachines of α1, α2 and β subunits is described.

High-level synthesis and secretion of laccase, a metalloenzyme biocatalyst, by the halophilic archaeon Haloferax volcanii

Haloarchaea and their enzymes have extremophilic properties desirable for use as platform organisms and biocatalysts in the bioindustry. These GRAS (generally regarded as safe) designated microbes thrive in hypersaline environments and use a salt-in strategy to maintain osmotic homeostasis. This unusual strategy has resulted in the evolution of most of the intracellular and extracellular enzymes of haloarchaea to be active and stable not only in high salt (2-5M) but also in low salt (0.2M). This salt tolerance is correlated with a resilience to low water activity, thus, rendering the haloarchaeal enzymes active and stable in organic solvent and temperatures of 50-60°C used in the enzymatic biodelignification and saccharification of lignocellulosic materials. High-level secretion of haloarchaeal enzymes to the extracellular milieu is useful for many applications, including enzymes that deconstruct biomass to allow for lignin depolymerization and simultaneous fermentation of sugars released from hemicellulose and cellulose fractions of lignocellulosics. Here we detail strategies and methods useful for high-level secretion of a laccase, HvLccA, that mediates oxidation of various phenolics by engineering a recombinant strain of the haloarchaeon Haloferax volcanii.

Functional interrelationship between TFII-I and E2F transcription factors at specific cell cycle gene loci

Transcription factor TFII-I is a multifunctional protein implicated in the regulation of cell cycle and stress-response genes. Previous studies have shown that a subset of TFII-I associated genomic sites contained DNA-binding motifs for E2F family transcription factors. We analyzed the co-association of TFII-I and E2Fs in more detail using bioinformatics, chromatin immunoprecipitation, and co-immunoprecipitation experiments. The data show that TFII-I interacts with E2F transcription factors. Furthermore, TFII-I, E2F4, and E2F6 interact with DNA-regulatory elements of several genes implicated in the regulation of the cell cycle, including DNMT1, HDAC1, CDKN1C, and CDC27. Inhibition of TFII-I expression led to a decrease in gene expression and in the association of E2F4 and E2F6 with these gene loci in human erythroleukemia K562 cells. Finally, TFII-I deficiency reduced the proliferation of K562 cells and increased the sensitivity toward doxorubicin toxicity. The results uncover novel interactions between TFII-I and E2Fs and suggest that TFII-I mediates E2F function at specific cell cycle genes.