The influence of Ala205 on the specificity of cathepsin L produced by dextran sulfate assisted activation of the recombinant proenzyme.

Human procathepsin L has been expressed in E. coli in the form of inclusion bodies. The recombinant protein was isolated, refolded and processed at pH 5.5 by the addition of dextran sulfate which increased the overall yield of cathepsin L almost 10-fold. After the auto-activation of the 38 kDa procathepsin L at least three processing sites were determined by N-terminal amino acid sequencing. After replacing the Ala205 residue by glutamic acid, cathepsin B-like specificity was introduced into cathepsin L. This mutation resulted in a 15-fold increased activity toward the substrate Z-Arg-Arg-AMC and in a 29-fold decreased activity toward Z-Phe-Arg-AMC. Residue 205 is thereby confirmed experimentally to be critical for the specificity of cathepsins B and L.

Crystal structures of human procathepsin B at 3.2 and 3.3 Angstroms resolution reveal an interaction motif between a papain-like cysteine protease and its propeptide.

A wild-type human procathepsin B was expressed, crystallized in two crystal forms and its crystal structure determined at 3.2 and 3.3 Angstroms resolution. The structure reveals that the propeptide folds on the cathepsin B surface, shielding the enzyme active site from exposure to solvent. The structure of the enzymatically active domains is virtually identical to that of the native enzyme [Musil et al. (1991) EMBO J. 10, 2321-2330]: the main difference is that the occluding loop residues are lifted above the body of the mature enzyme, supporting the propeptide structure.

Folding and activation of human procathepsin S from inclusion bodies produced in Escherichia coli.

Human procathepsin S was produced in the form of insoluble inclusion bodies in Escherichia coli using an inducible T7-based expression system. After cell disruption, the dissolved inclusion body proteins were S-sulphonated with 2-nitro-5-thiosulphobenzoate and purified by gel filtration. Recombinant procathepsin S was renatured at pH 7.6 by a two-step dilution which significantly increased the yield of production compared to single-step dilution. The proenzyme was autocatalytically processed to active cathepsin S at pH 4.5 in the presence of an excess of cysteine and catalytic amounts of dextran sulphate. Most of the loss of procathepsin S occurred during folding, probably because of aggregation. Concentrations lower than 20 microgram/ml of procathepsin S were necessary to minimise such aggregation. The recombinant cathepsin S was catalytically active on fluorogenic substrates and had kinetic properties similar to those of recombinant enzyme produced in yeast. The expression, renaturation, and activation procedures used enable the production of up to 2 mg of catalytically active recombinant human cathepsin S/l fermentation broth.

Expression of full-length human procathepsin L cDNA in Escherichia coli and refolding of the expression product.

From human embrional lung fibroblasts mRNA was obtained and converted to cDNA. The procathepsin L coding region was amplified by PCR, inserted into pALTER and, after checking the nucleotide sequence, transferred into pET81F1+. Procathepsin L was expressed by induction of recombinant E. coli strain BL21[DE3](pLysS) with IPTG and was found to be deposited into inclusion bodies. These were isolated and solubilized in guanidinium hydrochloride. The soluble proteins were sulphonated and procathepsin L was obtained after gel filtration. Purified proenzyme was refolded by dialysis and autoactivated into a form of the expected size and enzymatic activity against a fluorogenic substrate.

The preparation of catalytically active human cathepsin B from its precursor expressed in Escherichia coli in the form of inclusion bodies.

A cDNA clone encoding human procathepsin B was expressed at a high level in Escherichia coli using a T7 polymerase expression system, resulting in the formation of insoluble cytoplasmic protein aggregates (inclusion bodies). The recombinant product was solubilized and renatured by refolding and reoxidation. The proenzyme was subsequently processed with pepsin to produce an enzymically active enzyme. By systematic variation of the parameters influencing the folding, formation of disulphide bonds, and processing of procathepsin B to the catalytically active mature form, a simple renaturation procedure was designed, allowing the production of about 3 mg purified active cathepsin B/l E. coli culture broth. The enzyme obtained in this way consists of a single chain and, as a consequence of pepsin treatment, possesses a three-amino-acid extension at its N-terminus. The enzyme has similar kinetic and immunological properties to native human cathepsin B.

Isolation and characterisation of chicken L- and H-kininogens and their interaction with chicken cysteine proteinases and papain.

We have isolated L- and H-kininogens from chicken egg white and plasma using affinity chromatography on CM-papain Sepharose, Con-A Sepharose, gel filtration and ion exchange chromatography, in pure form. In chicken plasma mostly HK was present, whereas in chicken egg white both LK and HK were identified. The determined Mr of LK and HK were 69000 and about 96000, respectively. They occurred in multiple forms with pI 4.3-5.2. The inhibitory activity of chicken HK was tested against cysteine proteinases cathepsins B and L, isolated from chicken liver, and papain. The obtained Ki values demonstrated that chicken H-kininogen is a strong inhibitor of chicken cathepsin L and papain, but much weaker inhibitor of chicken cathepsin B.

Construction and cloning of recombinant rat trypstatin variants and their expression as fusion proteins in E. coli.

A synthetic master gene coding for rat trypstatin was designed, assembled of eight oligonucleotides, ligated into the cloning vector pUC8 and cloned in E. coli. In addition to the expected product DNA sequencing revealed the presence of several gene variants. The gene coding for (-1M F44G) rat trypstatin was mutated to a wild type form (-1M) rat trypstatin by cassette mutagenesis. For the first expression experiments the E. coli pEx31 system was used. After SDS-PAGE analysis fusion proteins were detected consisting of the N-terminal part of MS2-polymerase, a linker region and of the appropriate rat trypstatin variant. These fusion proteins were synthesized in amounts as high as 25% of total E. coli proteins.

(K15R M52E) aprotinin is a weak Kunitz-type inhibitor of HIV-1 replication in H9 cells.

The (K15R M52E) aprotinin is a recombinant molecule with a broader inhibition spectrum against serine proteinases and a higher affinity towards certain proteinases as compared to native aprotinin. This aprotinin variant was produced in E. coli, isolated and purified to homogeneity. The inhibitor was further tested for its effectiveness to reduce human immunodeficiency virus type 1 (HIV-1) replication. Virus growth was followed by an ELISA which detects the amount of virus core protein p24. At a concentration of 50 microM, the recombinant (K15R M52E) aprotinin clearly reduced HIV-1 replication in H9 cells.