Enzyme-linked immunosorbent assays for insulin-like growth factor-I using six-histidine tag fused proteins

Effects of L-arginine on refolding of lysine-tagged human insulin-like growth factor 1 expressed in Escherichia coli

Insulin-like growth factor 1 (IGF1), a therapeutic protein, is highly homologous to proinsulin in 3-dimensional structure. To highly express IGF1 in recombinant Escherichia coli, IGF1 was engineered to be fused with the 6-lysine tag and ubiquitin at its N-terminus (K6Ub-IGF1). Fed-batch fermentation of E. coli TG1/pAPT-K6Ub-IGF1 resulted in 60.8 g/L of dry cell mass, 18% of which was inclusion bodies composed of K6Ub-IGF1. Subsequent refolding processes were conducted using accumulated inclusion bodies. An environment of 50 mM bicine buffer (pH 8.5), 125 mM L-arginine, and 4 °C was chosen to optimize the refolding of K6Ub-IGF1, and 240 mg/L of denatured K6Ub-IGF1 was refolded with a 32% yield. The positive effect of L-arginine on K6Ub-IGF1 refolding might be ascribed to preventing unfolded K6Ub-IGF1 from undergoing self-aggregation and thus increasing its solubility. The simple dilution refolding, followed by cleavage of the fusion protein by site-specific UBP1 and chromatographic purification of IGF1, led production of authentic IGF1 with 97% purity and an 8.5% purification yield, starting from 500 mg of inclusion bodies composed of K6Ub-IGF1, as verified by various analytical tools, such as RP-HPLC, CD spectroscopy, MALDI-TOF mass spectrometry, and Western blotting. Thus, it was confirmed that L-arginine with an aggregation-protecting ability could be applied to the development of refolding processes for other inclusion body-derived proteins.

Exploiting the interactions between poly-histidine fusion tags and immobilized metal ions

Immobilized metal affinity chromatography (IMAC) of proteins containing poly-histidine fusion tags is an efficient research tool for purifying recombinant proteins from crude cellular feedstocks at laboratory scale. Nevertheless, to achieve successful purification of large amounts of the target protein for critical therapeutic applications that demand the precise removal of fusion tags, it is important to also take into consideration issues such as protein quality, efficiency, cost effectiveness, and optimal affinity tag choice and design. Despite the many considerations described in this article, it is expected that enhanced selectivity, the primary consideration in the field of protein separation, will continue to see the use of IMAC in solving new purification challenges. In addition, the platform nature of this technology makes it an ideal choice in purifying proteins with unknown properties. Finally, the unique interaction between immobilized metal ions and poly-histidine fusion tag has enabled new developments in the areas of biosensor, immunoassay, and other analytical technologies.

Surface plasmon resonance immuno assays - A perspective

Human growth hormone (GH) represents an extremely challenging task from an anti-doping viewpoint. GH is an endogenously produced substance, present at very low levels in circulation (for the most abundant 22kDa isoform approximately 50pM in plasma and 100fM in urine) either as monomer or homo- and heterodimers, comprises a family of distinct isoforms, and obeys a pulsatile secretion routine that is affected by many different internal and external factors. Upon administration of the recombinant, single-isoform pharmaceutical, the feedback mechanism reduces the endogenous heterogeneity resulting in altered ratios between the different GH isoforms. Thus, measuring the isoform ratios through immuno assays appears the approach of choice. Conventional assays do not provide information on isoform-specific association and dissociation events of the individual primary antibody-isoform or isoform-secondary antibody interactions. This particular information can be obtained using the technology of surface plasmon resonance (SPR) which enables monitoring of biomolecular interactions in a dynamic and label-free setting. In this paper the different aspects of SPR are described, how the technology may be beneficial for understanding today's anti-GH immunoassays, and whether the approach could be employed for measuring GH in the near future.