Characterization of two putative prolinases (PepR1 and PepR2) from Lactobacillus plantarum WCFS1: Occurrence of two isozymes with structural similarity and different catalytic properties

Post-Proline Cleaving Enzymes (PPCEs): Classification, Structure, Molecular Properties, and Applications

Proteases or peptidases are hydrolases that catalyze the breakdown of polypeptide chains into smaller peptide subunits. Proteases exist in all life forms, including archaea, bacteria, protozoa, insects, animals, and plants due to their vital functions in cellular processing and regulation. There are several classes of proteases in the MEROPS database based on their catalytic mechanisms. This review focuses on post-proline cleaving enzymes (PPCEs) from different peptidase families, as well as prolyl endoprotease/oligopeptidase (PEP/POP) from the serine peptidase family. To date, most PPCEs studied are of microbial and animal origins. Recently, there have been reports of plant PPCEs. The most common PEP/POP are members of the S9 family that comprise two conserved domains. The substrate-limiting β-propeller domain prevents unwanted digestion, while the α/β hydrolase catalyzes the reaction at the carboxyl-terminal of proline residues. PPCEs display preferences towards the Pro-X bonds for hydrolysis. This level of selectivity is substantial and has benefited the brewing industry, therapeutics for celiac disease by targeting proline-rich substrates, drug targets for human diseases, and proteomics analysis. Protein engineering via mutagenesis has been performed to improve heat resistance, pepsin-resistant capability, specificity, and protein turnover of PPCEs for pharmacological applications. This review aims to synthesize recent structure-function studies of PPCEs from different families of peptidases to provide insights into the molecular mechanism of prolyl cleaving activity. Despite the non-exhaustive list of PPCEs, this is the first comprehensive review to cover the biochemical properties, biological functions, and biotechnological applications of PPCEs from the diverse taxa.

Development of redox potential-driven fermentation process for recombinant protein expression

OBJECTIVES

A redox potential-driven fermentation, maintaining dissolved oxygen at a prescribed level while simultaneously monitoring the changes of fermentation redox potential, was developed to guide the cultivation progress of recombinant protein expression.

RESULTS

A recombinant E. coli harboring prolinase-expressing plasmid (pKK-PepR2) was cultivated using the developed process. Two distinct ORP valleys were noticeable based on recorded profile. The first ORP valley is equivalent to the timing for the addition of inducing agent, and the second ORP valley serves to guide the timing for cell harvesting. The final prolinase activity is 0.172 μmol/mg/min as compared to that of 0.154 μmol/mg/min where the optical density was employed to guide the timing of inducer addition and an empirically determined length of the cultivation.

CONCLUSION

The developed process can be further modified to become an automatic operation.

The relevance of probiotics in Caesarean-born neonates

There is growing interest in the use of probiotics in neonates. In particular, Lactobacillus rhamnosus, L. acidophilus, Bifidobacterium breve and B. longum have been well studied. Caesarean-section (CS)-born infants often lack Lactobacillus spp. and Bifidobacterium spp., which showed increasing evidence in establishing the neonatal immune system. Furthermore, CS increases the difficulties for mothers in initiating and sustaining breastfeeding. Increasing evidence shows CS-born infants are more susceptible to allergy, infections and chronic inflammatory diseases later in life. The number of CS births has increased continuously, now accounting for 35% of all deliveries Australia wide. In this context, probiotics may have a role in establishing a healthy neonatal gut microbiome.

High-level expression and molecular characterization of a recombinant prolidase from Escherichia coli NovaBlue

Long-term use of organophosphorus (OP) compounds has become an increasing global problem and a major threat to sustainability and human health. Prolidase is a proline-specific metallopeptidase that can offer an efficient option for the degradation of OP compounds. In this study, a full-length gene from Escherichia coli NovaBlue encoding a prolidase (EcPepQ) was amplified and cloned into the commercially-available vector pQE-30 to yield pQE-EcPepQ. The overexpressed enzyme was purified from the cell-free extract of isopropyl thio-β-D-galactoside IPTG-induced E. coli M15 (pQE-EcPepQ) cells by nickel-chelate chromatography. The molecular mass of EcPepQ was determined to be about 57 kDa by 12% sodium dodecyl sulfate–polyacrylamide gel electrophoresis and the result of size-exclusion chromatography demonstrated that the enzyme was mainly present in 25 mM Tris–HCl buffer (pH 8.0) as a dimeric form. The optimal conditions for EcPepQ activity were 60 °C, pH 8.0, and 0.1 mM Mn²⁺ ion. Kinetic analysis with Ala-Pro as the substrate showed that the K_m and k_cat values of EcPepQ were 8.8 mM and 926.5 ± 2.0 s⁻¹, respectively. The thermal unfolding of EcPepQ followed a two-state process with one well-defined unfolding transition of 64.2 °C. Analysis of guanidine hydrochloride (GdnHCl)-induced denaturation by tryptophan emission fluorescence spectroscopy revealed that the enzyme had a [GdnHCl]_0.5,N-U value of 1.98 M. The purified enzyme also exhibited some degree of tolerance to various water/organic co-solvents. Isopropanol and tetrahydrofuran were very detrimental to the enzymatic activity of EcPepQ; however, other more hydrophilic co-solvents, such as formamide, methanol, and ethylene glycol, were better tolerated. Eventually, the non-negative influence of some co-solvents on both catalytic activity and structural stability of EcPepQ allows to adjust the reaction conditions more suitable for EcPepQ-catalyzed bioprocess.

Effect of high pressure on structural modifications and enzymatic activity of a purified X-prolyl dipeptidyl aminopeptidase from Streptococcus thermophilus

PepX aminopeptidase from Streptococcus thermophilus ACA DC 0022, used in Greek Feta cheese manufacturing, was purified. PepX comprises two subunits of equal molecular mass estimated, using SDS-PAGE and native-PAGE electrophoresis, to be 86 kDa. The effects of high pressure processing (100-450 MPa, combined with 20-40 °C) on purified PepX activity and structure were studied. Activation of the enzyme was observed after processing at 100-200 MPa and 20-30 °C. More intense processing conditions led to enzyme inactivation. PepX HP-induced conformational changes were also investigated through application of Circular Dichroism spectroscopy (CD). Pressures up to 200 MPa resulted in a structurally molten globule-like state where PepX maintained its secondary structure but the tertiary structure was substantially affected and enzyme activity increased. Both secondary and tertiary structures were affected severely by higher pressures (450 MPa), which reduced enzyme activity.