Purification of recombinant soluble forms of furin produced in Chinese hamster ovary cells

Corin is present in the normal human heart, kidney, and blood, with pro-B-type natriuretic peptide processing in the circulation

BACKGROUND

B-type natriuretic peptide (BNP), which is activated in heart failure (HF), is processed to an active form by corin. The corin gene is expressed in the human heart and kidney, but corin protein expression in the heart, kidney, and circulation, along with whether proBNP is processed by circulating corin, remains unknown.

METHODS

We examined corin protein expression by immunostaining and Western blot in human heart and kidney, and we assessed the circulating corin concentration by ELISA. We examined histidine-tagged (His-tag) proBNP(1-108) processing in serum and plasma by immunoprecipitation and Western blot and sequenced the processed form.

RESULTS

Normal human heart and kidney displayed the presence of corin, especially in cells around the vasculature. Both corin and proBNP(1-108) were present in the plasma of healthy human subjects, with circulating corin significantly higher in men than women (P < 0.0001) and a positive correlation of corin to age (P = 0.0497, r = 0.27). In fresh normal plasma and serum, His-tag proBNP(1-108) was processed to a lower molecular weight form confirmed to be BNP. Processed BNP was higher in men than women (P = 0.041) and was positively correlated to plasma corin concentrations (P = 0.041, r = 0.65).

CONCLUSIONS

Our results support the concept that proBNP(1-108) may be processed outside of the heart in the circulation where the proprotein convertase is present. Moreover, sex may impact this process, since corin concentrations are higher in men. These findings may have important physiologic and pathophysiologic implications for the proBNP/corin system in the human.

Axonal transports of Boc-Gly-Arg-Arg-MCA hydrolysing enzyme in rat sciatic nerves

Study on neural axon transport is a very useful method to find a neuron-specific protease. In the present study, the enzyme activity (release of 7-amino-4-methyl-coumarin from t-butyloxycarbonyl-glycyl-L-arginyl-L-arginine-4-methylcoumaryl-7-amide) was measured in the proximal, middle, and distal segments between 12 and 120 h after double ligations of rat sciatic nerves to find precursor processing enzyme specific for pair of basic amino acid residue. The enzyme activity was significantly increased not only in the proximal but also in the distal segments 12-120 h after the ligation, and the maximal enzyme activity was found in both segments at 72 h. The enzyme activity eluted by anion exchange chromatography of the proximal segment showed at least three peaks, and was slightly higher than the activity of the distal one. The activity in the middle segment was very low in comparison with the activity in the proximal and distal segments. These data indicate that some of the enzymes specific for pair of basic amino acid residue are transported by both anterograde and retrograde axonal flow, and may undergo a neuron-specific processing.

Eukaryotic protein processing: endoproteolysis of precursor proteins

Limited endoproteolysis of biologically inactive polypeptide precursors is a general mechanism generating a diversity of biologically active peptides and proteins in all eukaryotic phyla. One of the major recognition motifs involves cleavage at either specific single or pairs of basic residues of the general formula (R/K) - Xn - (R/K) decreases, where n = 0, 2, 4 or 6. Such sites are found in a variety of protein precursors in all eukaryotes, including those of endocrine and neural polypeptide hormones, enzymes, growth factors, receptors, adhesion molecules, viral glycoproteins, coagulation factors and even cell signaling molecules. A family of seven mammalian proteinases responsible for the processing of these proproteins has been recently identified. It comprises the proprotein convertases PC1/PC3, PC2, furin/PACE, PC4, PACE4, PC5/PC6 and PC7/SPC7/LPC/PC8. In a combinatorial fashion, these enzymes determine the cell-type and time at which biologically active products are derived from a given inactive precursor protein, thereby profoundly affecting cellular communication, differentiation and metabolic activity.

Monitoring proteolysis of recombinant human interferon-gamma during batch culture of Chinese hamster ovary cells

Proteolytic cleavage of recombinant human interferon-gamma (IFN-gamma) expressed in Chinese hamster ovary (CHO) cells during batch fermentation has been monitored by mass spectrometric peptide mapping. IFN-gamma was purified from cell-free culture supernatant by immunoaffinity chromatography and cleaved by endoprotease Asp-N. Peptide fragments were resolved by reverse-phase HPLC and identified by a combination of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) and automated N-terminal peptide sequencing. Using this approach, a peptide was identified as the C-terminal fragment of the IFN-gamma polypeptide. Analysis of this peptide by MS indicated that the recombinant IFN-gamma polypeptide secreted by CHO cells was truncated by at least ten amino acids, initially at Gln133-Met134. No full length (143 amino acids) polypeptide molecules were observed at any stages of the fermentation. Additional proteolytic cleavages at basic amino acids N-terminal of Gln133 occurred during the later stages of the culture resulting in a heterogeneous IFN-gamma polypeptide with "ragged" C-termini.

Role of physiology in the determination of protein heterogeneity

One of the major problems faced in the manufacture of recombinant proteins is the assessment and control of product heterogeneity, which is caused mainly by the biological variation in post-translational processing. The past year has witnessed significant improvements both in analytical methods for detecting variation in this processing and in our ability to control it.