The efficiency of processing and secretion of the thermolysin-like neutral protease from Bacillus cereus does not require the whole prosequence, but does depend on the nature of the amino acid sequence in the region of the cleavage site

Gain-of-function Shh mutants activate Smo cell-autonomously independent of Ptch1/2 function

Sonic Hedgehog (Shh) signaling is characterized by non-cell autonomy; cells expressing Shh do not respond to the ligand. Here, we identify several Shh mutations that can activate the Hedgehog (Hh) pathway cell-autonomously. Cell-autonomous pathway activation requires the extracellular cysteine rich domain of Smoothened, but is otherwise independent of the Shh receptors Patched1 and -2. Many of the Shh mutants that gain activity fail to undergo auto processing resulting in the perdurance of the Shh pro-peptide, a form of Shh that is sufficient to activate the Hh response cell-autonomously. Our results demonstrate that Shh is capable of activating the Hh pathway via Smoothened, independently of Patched1/2, and that it harbors an intrinsic mechanism that prevents cell-autonomous activation of the Shh response.

Propeptides as modulators of functional activity of proteases

Most proteases are synthesized in the cell as precursor-containing propeptides. These structural elements can determine the folding of the cognate protein, function as an inhibitor/activator peptide, mediate enzyme sorting, and mediate the protease interaction with other molecules and supramolecular structures. The data presented in this review demonstrate modulatory activity of propeptides irrespective of the specific mechanism of action. Changes in propeptide structure, sometimes minor, can crucially alter protein function in the living organism. Modulatory activity coupled with high variation allows us to consider propeptides as specific evolutionary modules that can transform biological properties of proteases without significant changes in the highly conserved catalytic domains. As the considered properties of propeptides are not unique to proteases, propeptide-mediated evolution seems to be a universal biological mechanism.

Extracellular expression of a functional recombinant Ganoderma lucidium immunomodulatory protein by Bacillus subtilis and Lactococcus lactis

Bacillus subtilis and Lactococcus lactis are ideal hosts for the production of extracellular heterologous proteins of major commercial importance. A recombinant gene for the novel Ganoderma lucidium immunomodulatory protein LZ-8, recombinant LZ-8, was designed encoding the same amino acid sequence but using the preferred codons for both strains and was synthesized by overlapping extension PCR. Using the signal peptide (SP) from subtilisin YaB (SP(YaB)), recombinant LZ-8 was expressed extracellularly in Bacillus subtilis and Lactococcus lactis. In the absence of SP(YaB), recombinant LZ-8 was expressed extracellularly in B. subtilis, but not in L. lactis. The three expressed recombinant LZ-8s showed different capacities for modulating the production of Th1 and Th2 cytokines by peripheral blood mononuclear cells and of tumor necrosis factor alpha by a macrophage cell line.

Mutational analysis of the autoprocessing site of subtilisin YaB-G124A

The potential residue at the autoprocessing site for improving processing efficiency was evaluated from hydrolysis of 19 cleavage-site-mimicking octapeptides, VTTXQTVP (-4 to +4), by the mature subtilisin YaB and YaB-G124A mutants. Both enzymes cleaved the octapeptides mainly at two sites, X-Q (A-site) and Q-T (B-site), at varied preferences. Based on the results above, Met(-1) of YaB-G124A was mutated and, as expected, extracellular enzyme production increased with Gln or Ala replacement, but decreased with Ile or Asp substitution. Together with previous structural studies, our results suggest that autoprocessing is dependent on not only the primary structure, but also the peptide flexibility around the processing site. Cleavage at the B-site resulted in a novel YaB mutant lacking the N-terminus Gln 1, which led the mutant enzyme to less enzymatic activity by 80% and less thermal stability by 20 degrees C, perhaps due to its ligation to the high-affinity calcium ion.

Substrate specificity in the highly heterogeneous M4 peptidase family is determined by a small subset of amino acids

The members of the M4 peptidase family are involved in processes as diverse as pathogenicity and industrial applications. For the first time a number of M4 family members, also known as thermolysin-like proteases, has been characterized with an identical substrate set and a uniform set of assay conditions. Characterization with peptide substrates as well as high performance liquid chromatography analysis of beta-casein digests shows that the M4 family is a homogeneous family in terms of catalysis, even though there is a significant degree of amino acid sequence variation. The results of this study show that differences in substrate specificity within the M4 family do not correlate with overall sequence differences but depend on a small number of identifiable amino acids. Indeed, molecular modeling followed by site-directed mutagenesis of one of the substrate binding pocket residues of the thermolysin-like proteases of Bacillus stearothermophilus converted the catalytic characteristics of this variant into that of thermolysin.

Elastase and the LasA protease of Pseudomonas aeruginosa are secreted with their propeptides

Pseudomonas aeruginosa elastase and the LasA protease are synthesized as preproenzymes with long amino-terminal propeptides. The elastase propeptide is cleaved autocatalytically in the periplasm to form a transient, inactive elastase-propeptide complex. In contrast, the processing of proLasA does not involve autoproteolysis. In this study, we analyzed short-term P. aeruginosa cultures under conditions that minimize proteolysis and found that an elastase-propeptide complex is secreted, and then the propeptide is degraded extracellularly, apparently by elastase itself. LasA protease, on the other hand, was found to be secreted in its unprocessed 42-kDa proenzyme form. The processing of proLasA occurred extracellularly, and it involved the transient appearance of a 28-kDa intermediate and the respective 14-kDa LasA propeptide fragment. The processing of proLasA in P. aeruginosa strain FRD740, which does not express elastase, also proceeded via the 28-kDa intermediate, but the rate of processing was greatly reduced. This low rate of proLasA processing was further reduced when the activity of a secreted lysine-specific protease was blocked. Purified secreted proteases of P. aeruginosa (i.e. elastase, the lysine-specific protease, and alkaline proteinase) converted proLasA to the active enzyme. Processing by elastase and the lysine-specific enzyme, but not by alkaline proteinase, proceeded via the 28-kDa intermediate, and both were far more effective than alkaline proteinase in converting proLasA to the mature enzyme. We conclude that LasA protease and elastase are secreted with their propeptides, which are then degraded by secreted proteases of P. aeruginosa. In addition to their other functions, the propeptides may play a role in targeting their respective enzymes across the outer membrane.

Intramolecular processing of prothermolysin

Thermolysin, an extracellular zinc endopeptidase from Bacillus thermoproteolyticus, is synthesized as a pre-proenzyme and the prosequence has been shown to assist the refolding of the denatured enzyme in vitro and to inhibit enzyme activity (O'Donohue, M. J., and Beaumont, A. (1996) J. Biol. Chem. 271, 26477-26481). To determine whether prosequence cleavage from the mature enzyme is autocatalytic and if so, whether it is an intermolecular or intramolecular process, N-terminal histidine-tagged prothermolysin was expressed in Escherichia coli. Although partial processing to mature enzyme occurred, most of the proenzyme was recovered intact from inclusion bodies. This was then solubilized in guanidinium hydrochloride, immobilized on a cobalt-containing resin, and after dialysis against renaturation buffer, was quantitatively transformed to mature enzyme. However, when a mutation was introduced into the mature sequence to inactivate thermolysin, the proenzyme was not processed either in vivo or in vitro. In addition, mutated prothermolysin was not processed by exogenous thermolysin under a variety of experimental conditions. The results demonstrate that thermolysin maturation can proceed via an autocatalytic intramolecular pathway.

The roles of the prosequence of thermolysin in enzyme inhibition and folding in vitro

The zinc endopeptidase thermolysin (EC 3.4.24.27), an extracellular enzyme from Bacillus thermoproteolyticus, is synthesized as a preproprotein, with the prosequence (204 residues) being two-thirds the size of the mature enzyme (316 residues). This prosequence, expressed in and purified from Escherichia coli, inhibited thermolysin in vitro with an IC50 value of 14 nM. It also inhibited a closely related enzyme produced by Bacillus stearothermophillus, albeit with a 16-fold higher IC50 value (220 nM). The IC50 value for thermolysin inhibition was also increased 15-fold (210 nm) by a monoclonal antibody that recognizes an epitope close to, but not forming a part of, the active site. At a prosequence concentration of 5 microM a mammalian, thermolysin-like enzyme, neutral endopeptidase 24.11, was not inhibited. The prosequence appeared to act as a mixed, noncompetitive inhibitor of thermolysin activity, with a Ki value of 6 nM for its interaction with the enzyme alone and a Ki' value of 20 nM for its interaction with the enzyme-substrate complex. In addition, when thermolysin was denatured in 6 M guanidinium hydrochloride at acid pH and then brought to neutral pH by rapid dilution, the prosequence was found to facilitate the recovery of active enzyme in a stoichiometric manner.