Cloning and sequencing of the gene encoding X-prolyl-dipeptidyl aminopeptidase (PepX) from Streptococcus thermophilus strain ACA-DC 4

The Potential Role of the Dipeptidyl Peptidase-4-Like Activity From the Gut Microbiota on the Host Health

The Dipeptidyl peptidase-4 (DPP-4) activity influences metabolic, behavioral and intestinal disorders through the cleavage of key hormones and peptides. Some studies describe the existence of human DPP-4 homologs in commensal bacteria, for instance in Prevotella or Lactobacillus. However, the role of the gut microbiota as a source of DPP-4-like activity has never been investigated. Through the comparison of the DPP-4 activity in the cecal content of germ-free mice (GFM) and gnotobiotic mice colonized with the gut microbiota of a healthy subject, we bring the proof of concept that a significant DPP-4-like activity occurs in the microbiota. By analyzing the existing literature, we propose that DPP-4-like activity encoded by the intestinal microbiome could constitute a novel mechanism to modulate protein digestion as well as host metabolism and behavior.

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.

Proline iminopeptidase PepI overexpressing Lactobacillus casei as an adjunct starter in Edam cheese

In this study the growth of genetically modified Lactobacillus casei LAB6, overexpressing proline iminopeptidase PepI and its capacity to increase free proline was investigated during ripening of Edam cheese. The strain successfully survived 12 weeks of ripening period in cheese. The food-grade plasmid pLEB604, carrying the pepI gene, was stable, and PepI enzyme was active in LAB6 cells isolated at different stages of the ripening process. However, HPLC analyses indicated that Lb. casei LAB6 could not increase the amount of free proline in ripened cheese.

Extracellular production and characterization of Streptomyces X-prolyl dipeptidyl aminopeptidase

X-prolyl dipeptidyl aminopeptidases (X-PDAPs) are useful in various food industries. In this study, we performed sequence-based screening to obtain a stable X-PDAP enzyme from thermophilic Streptomyces strains. We found three genes that encoded X-PDAP from Streptomyces thermoluteus subsp. fuscus NBRC 14270 (14270 X-PDAP), Streptomyces thermocyaneoviolaceus NBRC 14271 (14271 X-PDAP), and Streptomyces thermocoerulescens NBRC 14273, which were subsequently cloned and sequenced. The deduced amino acid sequences of these genes showed high similarity, with ~80% identity with each other. The isolated X-PDAPs and an X-PDAP from Streptomyces coelicolor were expressed in Streptomyces lividans using a hyperexpression vector: pTONA5a. Among these genes, only 14270 and 14271 X-PDAPs caused overexpression and extracellular production without artificial signal peptides. We also characterized the biochemical properties of purified 14271 X-PDAP. In addition, we found that, in peptide synthesis via an aminolysis reaction, this enzyme recognized D-amino acid derivatives as acyl acceptors, similar to L-amino acid derivatives.

Biotechnological methods to accelerate cheddar cheese ripening

Cheese is one of the dairy products that can result from the enzymatic coagulation of milk. The basic steps of the transformation of milk into cheese are coagulation, draining, and ripening. Ripening is the complex process required for the development of a cheese's flavor, texture and aroma. Proteolysis, lipolysis and glycolysis are the three main biochemical reactions that are responsible for the basic changes during the maturation period. As ripening is a relatively expensive process for the cheese industry, reducing maturation time without destroying the quality of the ripened cheese has economic and technological benefits. Elevated ripening temperatures, addition of enzymes, addition of cheese slurry, attenuated starters, adjunct cultures, genetically engineered starters and recombinant enzymes and microencapsulation of ripening enzymes are traditional and modern methods used to accelerate cheese ripening. In this context, an up to date review of Cheddar cheese ripening is presented.

Proteolytic systems of lactic acid bacteria

Lactic acid bacteria (LAB) have a very long history of use in the manufacturing processes of fermented foods and a great deal of effort was made to investigate and manipulate the role of LAB in these processes. Today, the diverse group of LAB includes species that are among the best-studied microorganisms and proteolysis is one of the particular physiological traits of LAB of which detailed knowledge was obtained. The proteolytic system involved in casein utilization provides cells with essential amino acids during growth in milk and is also of industrial importance due to its contribution to the development of the organoleptic properties of fermented milk products. For the most extensively studied LAB, Lactococcus lactis, a model for casein proteolysis, transport, peptidolysis, and regulation thereof is now established. In addition to nutrient processing, cellular proteolysis plays a critical role in polypeptide quality control and in many regulatory circuits by keeping basal levels of regulatory proteins low and removing them when they are no longer needed. As part of the industrial processes, LAB are challenged by various stress conditions that are likely to affect metabolic activities, including proteolysis. While environmental stress responses of LAB have received increasing interest in recent years, our current knowledge on stress-related proteolysis in LAB is almost exclusively based on studies on L. lactis. This review provides the current status in the research of proteolytic systems of LAB with industrial relevance.

Proteome analysis of Streptococcus thermophilus grown in milk reveals pyruvate formate-lyase as the major upregulated protein

We investigated the adaptation to milk of Streptococcus thermophilus LMG18311 using a proteomic approach. Two-dimensional electrophoresis of cytosolic proteins were performed after growth in M17 medium or in milk. A major modification of the proteome concerned proteins involved in the supply of amino acids, like the peptidase PepX, and several enzymes involved in amino acid biosynthesis. In parallel, we observed the upregulation of the synthesis of seven enzymes directly involved in the synthesis of purines, as well as formyl-tetrahydrofolate (THF) synthetase and serine hydroxy-methyl transferase, two enzymes responsible for the synthesis of compounds (THF and glycine, respectively) feeding the purine biosynthetic pathway. The analysis also revealed a massive increase in the synthesis of pyruvate formate-lyase (PFL), the enzyme which converts pyruvate into acetyl coenzyme A and formate. PFL has been essentially studied for its role in mixed-acid product formation in lactic acid bacteria during anaerobic fermentation. However, formate is an important methyl group donor for anabolic pathway through the formation of folate derivates. We hypothesized that PFL was involved in purine biosynthesis during growth in milk. We showed that PFL expression was regulated at the transcriptional level and that pfl transcription occurred during the exponential growth phase in milk. The complementation of milk with formate or purine bases was shown to reduce pfl expression, to suppress PFL synthesis, and to stimulate growth of S. thermophilus. These results show a novel regulatory mechanism controlling the synthesis of PFL and suggest an unrecognized physiological role for PFL as a formate supplier for anabolic purposes.

ThyA as a selection marker in construction of food-grade host-vector and integration systems for Streptococcus thermophilus

We constructed food-grade host-vector and integration systems for Streptococcus thermophilus by using a thymidylate synthase gene (thyA) as the selection marker. Two thyA genes, thyA(St) and thyA(Lb), were cloned from S. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, respectively. Thymidine-requiring mutants of S. thermophilus were obtained after successive cultures in the presence of trimethoprim, and one of them, TM1-1, was used as the host. Food-grade vectors were constructed by using either thyA(St) or thyA(Lb) as the selection marker. Transformants of TM1-1 created by using these vectors were selected for thymidine autotrophy as efficiently as for erythromycin resistance. By using the host-vector system developed in this way, a foreign amylase gene (amyA) was expressed in TM1-1 and was also integrated into the chromosome by use of a temperature-sensitive integration vector constructed with thyA(Lb) as the selection marker via a double-crossover event. The results obtained show that thyA is an efficient and safe selection marker for S. thermophilus that is suitable for food applications.

Effect of a bacterial pheromone peptide on host chemokine degradation in group A streptococcal necrotising soft-tissue infections

BACKGROUND

Necrotising soft-tissue infections due to group A streptococcus (GAS) are rare (about 0.2 cases per 100000 people). The disease progresses rapidly, causing severe necrosis and hydrolysis of soft tissues. Histopathological analysis of necrotic tissue debrided from two patients (one with necrotising fasciitis and one with myonecrosis) showed large quantities of bacteria but no infiltrating neutrophils. We aimed to investigate whether the poor neutrophil chemotaxis was linked with the ability of group A streptococcus (GAS) to degrade host chemokines.

METHODS

We did RT-PCR, ELISA, and dot-blot assays to establish whether GAS induces synthesis of interleukin 8 mRNA, but subsequently degrades the released chemokine protein. Class-specific protease inhibitors were used to characterise the protease that degraded the chemokine. We used a mouse model of human soft-tissue infections to investigate the pathogenic relevance of GAS chemokine degradation, and to test the therapeutic effect of a GAS pheromone peptide (SilCR) that downregulates activity of chemokine protease.

FINDINGS

The only isolates from the necrotic tissue were two beta-haemolytic GAS strains of an M14 serotype. A trypsin-like protease released by these strains degraded human interleukin 8 and its mouse homologue MIP2. When innoculated subcutaneously in mice, these strains produced a fatal necrotic soft-tissue infection that had reduced neutrophil recruitment to the site of injection. The M14 GAS strains have a missense mutation in the start codon of silCR, which encodes a predicted 17 aminoacid pheromone peptide, SilCR. Growth of the M14 strain in the presence of SilCR abrogated chemokine proteolysis. When SilCR was injected together with the bacteria, abundant neutrophils were recruited to the site of infection, bacteria were cleared without systemic spread, and the mice survived. The therapeutic effect of SilCR was also obtained in mice challenged with M1 and M3 GAS strains, a leading cause of invasive infections.

INTERPRETATION

The unusual reduction in neutrophils in necrotic tissue of people with GAS soft-tissue infections is partly caused by a GAS protease that degrades interleukin 8. In mice, degradation can be controlled by administration of SilCR, which downregulates GAS chemokine protease activity. This downregulation increases neutrophil migration to the site of infection, preventing bacterial spread and development of a fulminant lethal systemic infection.