A novel assay for the determination of PreScission protease by capillary electrophoresis

The detection of protease activity in the body plays a significant role in the early diagnosis of diseases. However, enzymes inevitably come into contact with various complex biological fluids in the body during the flow, which greatly increases the detection difficulty. Therefore, protease detection in vivo has great challenges. Herein, we report a new assay for detecting protease using capillary electrophoresis inside a capillary with semicircular bends. We first designed a peptide substrate, and then the peptide was self-assembled with quantum dots to form a QDs-peptide substrate. The capillary was bent to semicircular-shaped turns and served as a micro-reactor to allow protease and substrate react in it. Due to the different electrophoretic velocity, the protease and the substrate were mixed inside the bent capillary with sequential injections and the cleavage of the substrate can be detected using capillary electrophoresis combined with Förster resonance energy transfer technology. This novel assay will greatly expand the detection of enzyme activity in vivo.

NT*-HRV3CP: An optimized construct of human rhinovirus 14 3C protease for high-yield expression and fast affinity-tag cleavage

The human rhinovirus 14 3C protease (HRV3C protease), in fusion with glutathione S-transferase also referred to as PreScission™ protease, is a cysteine protease of particular interest for affinity tag removal from fusion proteins due to its stringent recognition sequence specificity (LEVLFQ/GX) and superior activity at low temperature. Here we report the expression, purification and use of a fusion construct of HRV3C protease, NT*-HRV3CP, that affords high expression yield in E. coli (over 300 mg/L cell culture), facile single-step purification, high solubility (>10 mg/mL) and excellent storage properties. NT*-HRV3CP cleaves affinity tags at 4 °C in minutes, making it an attractive tool for the production of recombinant proteins for biotechnological, industrial and pharmaceutical applications.

Single-step protease cleavage elution for identification of protein-protein interactions from GST pull-down and mass spectrometry

The study of protein-protein interactions is a major theme in biological disciplines. Pull-down or affinity-precipitation assays using GST fusion proteins have become one of the most common and valuable approaches to identify novel binding partners for proteins of interest (bait). Non-specific binding of prey proteins to the beads or to GST itself, however, inevitably complicates and impedes subsequent analysis of pull-down results. A variety of measures, each with inherent advantages and limitations, can minimise the extent of the background. This technical brief details and tests a modification of established GST pull-down protocols. By specifically eluting only the bait (minus the GST tag) and the associated non-specific binding proteins with a simple, single-step protease cleavage, a cleaner platform for downstream protein identification with MS is established. We present a proof of concept for this method, as evidenced by a GST pull-down/MS case study of the small guanosine triphosphatase (GTPase) Rab31 in which: (i) sensitivity was enhanced, (ii) a reduced level of background was observed, (iii) distinguishability of non-specific contaminant proteins from genuine binders was improved and (iv) a putative new protein-protein interaction was discovered. Our protease cleavage step is readily applicable to all further affinity tag pull-downs.

Easy and efficient protocol for purification of recombinant peptides

Peptide synthesis and purification remains a challenge. Low abundance leads to small yields when peptides are purified from natural sources. On the other hand, synthetic methods are limited by the chemical properties of the amino acids and the concurrent aggregation of peptides. In this paper, we report a versatile, high yielding and general purification method for randomly chosen recombinant peptides of variable sizes (ranging from ∼1.7kDa to ∼10kDa). Expressed as fusion proteins with commonly used tag proteins, these peptides are cleaved by 'PreScission protease' in a volatile buffer that makes concentration and recovery of the peptide easy. Separation of the cleaved peptide is achieved by selective precipitation of the larger tag protein with acetonitrile; leaving the peptide in solution. Our protocol can be used to generate a wide variety of peptides in significant quantities for biochemical, biophysical and physiological studies.