Steady-state kinetic analysis of human ubiquitin-activating enzyme (E1) using a fluorescently labeled ubiquitin substrate.

We report the synthesis of fluorescently labeled ubiquitin (Ub) and its use for following ubiquitin transfer to various proteins. Using Oregon green (Og) succinimidyl ester, we prepared a population of Ub mainly labeled by a single Og molecule; greater than 95% of the Og label is associated with Lys 6 of Ub. We demonstrate that Og-Ub is efficiently accepted by Ub-utilizing enzymes, such as the human ubiquitin-activating enzyme (E1). We used this fluorescent substrate to follow the steady-state kinetics of human E1-catalyzed Ub-transfer to the ubiquitin-carrier enzyme Ubc4. In this reaction, E1 uses three substrates: ATP, Ubc4, and Ub. The steady-state kinetics of Og-Ub utilization by E1 is presented. We have also used analytical ultracentrifugation methods to establish that E1 is monomeric under our assay condition (low salt) as well as under physiological condition (150 mM NaCl).

Production and purification of human fibroblast collagenase (MMP-1) expressed in the methylotrophic yeast Pichia pastoris.

The cDNA that encodes the proenzyme form of human fibroblast collagenase (proMMP-1) was expressed in the methylotrophic yeast Pichia pastoris. The proMMP-1 encoding DNA was fused to the Saccharomyces cerevisiae pre-pro alpha-mating factor secretion signal in the P. pastoris pPIC9 expression plasmid, transformed into strain GS115 (His-), and His+ Muts (slow methanol utilization) transformants were selected. Full-length proenzyme and processed forms of the protein could be detected in yeast culture supernatants following shake flask and 10-liter fermentations. The protein was purified to greater than 95% homogeneity. The recombinant proMMP-1 was comparable to the native fibroblast material based on (i) migration of the full-length molecule as a 52-kDa protein on reducing SDS-PAGE, (ii) correct N-terminal amino acid sequence, (iii) activation of the full-length molecule by 4-amino-phenylmercuric acetate to yield processed protein species, (iv) degradation of gelatin as monitored by zymogram gels, and (v) enzymatic activity. These data suggest that the P. pastoris expression system offers a convenient and efficient means to produce and purify MMP-1.

Production of human matrix metalloproteinase 3 (stromelysin) in Escherichia coli.

Full-length human matrix metalloproteinase 3 (prostomelysin or proMMP-3) was produced in Escherichia coli as an intracellular insoluble aggregate that could be solubilized and refolded to yield an activatable proenzyme. The refolded protein was purified to > 95% homogeneity. The recombinant proMMP-3 (re-proMMP-3) could be activated by agents known to stimulate self-catalyzed cleavage of native fibroblast proMMP-3. The N-terminal amino-acid sequence of the re-proMMP-3 and its activation products indicated that they were the same as those obtained with the natural material.

Purification and characterization of active and latent forms of recombinant plasminogen activator inhibitor 1 produced in Escherichia coli.

Plasminogen activator inhibitor 1 (PAI-1), the principal physiological inhibitor of tissue plasminogen activator (tPA), is a protein of 379 amino acids and belongs to the SERPIN family of serine protease inhibitors. We have previously described methods to express [Sisk et al. (1990) Gene 96, 305-309] and purify [Reilly et al. (1990) J. Biol. Chem. 265, 9570-9574] a highly active form of the protein in substantial amounts, from Escherichia coli. Further analyses of this material showed the presence of small but significant amounts of latent rPAI-1. The present paper describes for the first time purification of latent and active forms of rPAI-1 from a single preparation, as well as the functional and structural characteristics of the two forms. Latent rPAI-1, which has properties similar to the latent forms described by other groups, was separated from active rPAI-1 by high-resolution ion-exchange chromatography or by affinity chromatography using immobilized anhydrotrypsin. It had low intrinsic activity (< 5% of active rPAI-1) and was partially reactivated by guanidine hydrochloride treatment or by incubation with vitronectin. Conversion of the active rPAI-1 to the latent form was influenced by temperature and additives including sucrose, EDTA, and arginine. Active and latent rPAI-1 did not show any obvious differences in their primary structures and displayed remarkably similar secondary structures as determined by circular dichroism spectral analyses. However, they did exhibit differences in tryptophan fluorescence, suggesting tertiary structural differences between the two forms.