High yield expression in Pichia pastoris of human neutrophil elastase fused to cytochrome B5

Recombinant human neutrophil elastase (rHNE), a serine protease, was expressed in Pichia pastoris. Glycosylation sites were removed via bioengineering to prevent hyper-glycosylation (a common problem with this system) and the cDNA was codon optimized for translation in Pichia pastoris. The zymogen form of rHNE was secreted as a fusion protein with an N-terminal six histidine tag followed by the heme binding domain of Cytochrome B5 (CytB5) linked to the N-terminus of the rHNE sequence via an enteropeptidase cleavage site. The CytB5 fusion balanced the very basic rHNE (pI = 9.89) to give a colored fusion protein (pI = 6.87), purified via IMAC. Active rHNE was obtained via enteropeptidase cleavage, and purified via cation exchange chromatography, resulting in a single protein band on SDS PAGE (Mr = 25 KDa). Peptide mass fingerprinting analysis confirmed the rHNE amino acid sequence, the absence of glycosylation and the absence of an 8 amino acid C-terminal peptide as opposed to the 20 amino acids usually missing from the C-terminus of native enzyme. The yield of active rHNE was 0.41 mg/L of baffled shaker flask culture medium. Active site titration with alpha-1 antitrypsin, a potent irreversible elastase inhibitor, quantified the concentration of purified active enzyme. The Km of rHNE with methoxy-succinyl-AAPVpNA was identical with that of the native enzyme within the assay's limit of accuracy. This is the first report of full-length rHNE expression at high yields and low cost facilitating further studies on this major human neutrophil enzyme.

A Versatile and Robust Serine Protease Inhibitor Scaffold from Actinia tenebrosa

Serine proteases play pivotal roles in normal physiology and a spectrum of patho-physiological processes. Accordingly, there is considerable interest in the discovery and design of potent serine protease inhibitors for therapeutic applications. This led to concerted efforts to discover versatile and robust molecular scaffolds for inhibitor design. This investigation is a bioprospecting study that aims to isolate and identify protease inhibitors from the cnidarian Actinia tenebrosa. The study isolated two Kunitz-type protease inhibitors with very similar sequences but quite divergent inhibitory potencies when assayed against bovine trypsin, chymostrypsin, and a selection of human sequence-related peptidases. Homology modeling and molecular dynamics simulations of these inhibitors in complex with their targets were carried out and, collectively, these methodologies enabled the definition of a versatile scaffold for inhibitor design. Thermal denaturation studies showed that the inhibitors were remarkably robust. To gain a fine-grained map of the residues responsible for this stability, we conducted in silico alanine scanning and quantified individual residue contributions to the inhibitor's stability. Sequences of these inhibitors were then used to search for Kunitz homologs in an A. tenebrosa transcriptome library, resulting in the discovery of a further 14 related sequences. Consensus analysis of these variants identified a rich molecular diversity of Kunitz domains and expanded the palette of potential residue substitutions for rational inhibitor design using this domain.