Discontinuous polyacrylamide gel electrophoresis of cell wall proteinase from variants ofStreptococcus lactis

Proline-specific peptidases ofStreptococcus cremorisAM2

The present study identifies proline-specific peptidases found inStreptococcus cremorisAM2. These activities were present prcdominantly in the cytoplasmic fraction of the cells with minor amounts in cell membrane fraction. No evidence vvas found for such activities in either the extracellular fluid used to grow the cells, in the wash fraction or in the cell wall fraction. The involvement of these enzymes in release of free proline from proline-containing peptides is considered.

Genetics of the proteolytic system of lactic acid bacteria

The proteolytic system of lactic acid bacteria is of eminent importance for the rapid growth of these organisms in protein-rich media. The combined action of proteinases and peptidases provides the cell with small peptides and essential amino acids. The amino acids and peptides thus liberated have to be translocated across the cytoplasmic membrane. To that purpose, the cell contains specific transport proteins. The internalized peptides are further degraded to amino acids by intracellular peptidases. The world-wide economic importance of the lactic acid bacteria and their proteolytic system has led to an intensive research effort in this area and a considerable amount of biochemical data has been collected during the last two decades. Since the development of systems to genetically manipulate lactic acid bacteria, data on the genetics of enzymes and processes involved in proteolysis are rapidly being generated. In this review an overview of the latest genetic data on the proteolytic system of lactic acid bacteria will be presented. As most of the work in this field has been done with lactococci, the emphasis will, inevitably, be on this group of organisms. Where possible, links will be made with other species of lactic acid bacteria.

Molecular characterization of a cell wall-associated proteinase gene from Streptococcus lactis NCDO763

Streptococcus lactis NCDO763 harbours a plasmid designated pLP763. The cells harbouring pLP763 are able to grow to a higher density in milk because of their proteinase-positive phenotype (Prt+). The 6.2 kb HindIII-PstI fragment from pLP763 was found to be responsible for the Prt+ phenotype. The DNA fragment contains an incomplete large open reading frame (ORF). Further sequence analysis downstream from the PstI site revealed that the ORF consists of 5706 bases. It was found that the deduced amino acid sequence consisting of 1902 amino acid residues was extremely similar to that of the Wg2 proteinase, a serine protease from Streptococcus cremoris, suggesting that both genes were derived from a common ancestral gene.

Monoclonal Antibodies to the Cell-Wall-Associated Proteinase of Lactococcus lactis subsp. cremoris Wg2

Twelve monoclonal antibodies directed to the cell-wall-associated proteinase of Lactococcus lactis subsp. cremoris Wg2 were isolated after immunization of BALB/c mice with a partially purified preparation of the proteinase. The monoclonal antibodies reacted with the 126-kilodalton proteinase band in a Western immunoblot. All but one of the monoclonal antibodies reacted with protein bands with a molecular weight below 126,000, possibly degradation products of the proteinase. The monoclonal antibodies could be divided into six groups according to their different reactions with the proteinase degradation products in the Western blot. Different groups of monoclonal antibodies reacted with different components of the L. lactis subsp. cremoris Wg2 proteinase. Crossed immunoelectrophoresis showed that monoclonal antibody groups I, II, and III react with proteinase component A and that groups IV, V, and VI react with proteinase component B. The isolated monoclonal antibodies cross-reacted with the proteinases of other L. lactis subspecies. Monoclonal antibodies of group IV cross-reacted with proteinase component C of other L. lactis subsp. cremoris strains. The molecular weight of the proteinase attached to the cells of L. lactis subsp. cremoris Wg2 was 200,000, which is different from the previously reported values. This could be analyzed by immunodetection of the proteinase on a Western blot. This value corresponds to the molecular weight calculated from the amino acid sequence of the cloned L. lactis subsp. cremoris Wg2 proteinase gene.

Purification and Characterization of a Dipeptidase from Streptococcus cremoris Wg2

A dipeptidase was purified to homogeneity from a crude cell extract of Streptococcus cremoris Wg2 by DEAE-Sephacel column chromatography followed by preparative disc gel electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band with a molecular weight of 49,000. The dipeptidase is capable of hydrolyzing a range of dipeptides, but not peptides with longer chains. The enzyme was shown to be a metallo-Mn 2+ enzyme with a pH optimum of 8 and a temperature optimum of 50�C. The enzyme is strongly inhibited by thiol-reducing reagents but not by sulfhydryl reagents. Kinetic studies indicated that the enzyme has a relatively low affinity for leucyl-leucine and alanyl-alanine ( K m , 1.6 and 7.9 mM, respectively) but can hydrolyze these substrates at very high rates ( V max , 3,700 and 13,000 μmol/min per mg of protein, respectively).

Purification and characterization of a cell wall proteinase from Streptococcus lactis NCDO 763

A proteinase was purified from a cell wall extract of a culture of Streptococcus lactis NCDO 763 grown in skim milk. Being active at a low pH (at pH 4.8 on haemoglobin and pH 6.0-6.5 on casein) and completely inhibited by diisopropylfluorophosphate, it was considered to be a serine proteinase partly inhibited by EDTA; the mol. wt was approximately 80,000.

Cell Wall-Associated Proteases of Streptococcus cremoris Wg2

Two components of the proteolytic system, proteins A and B (J. Hugenholtz, F. Exterkate, and W. N. Konings, Appl. Environ. Microbiol. 48:1105-1110, 1984), have been studied in Streptococcus cremoris Wg2 by immunological methods. The components could not be separated by standard chromatography techniques because both proteins had almost identical molecular weights (about 140,000) and isoelectric points (pH 4.5). Specific antibodies were raised against proteins A and B by excision of the different immunoprecipitates from crossed immunoelectrophoresis gels. With these antibodies, protein A or B was removed from solutions containing both proteins. The purified proteins A and B possessed proteolytic activity and were inhibited by the serine protease inhibitor phenylmethylsulfonyl fluoride. Each of these proteins accounted for approximately 50% of the total proteolytic activity isolated from S. cremoris Wg2. The specific antibodies against the proteases were also used for immuno-gold labeling studies. The proteases were clearly seen to be located at the outside of the cell wall. The proteases had the same location when the genetic information coding for the proteases was cloned in Streptococcus lactis and Bacillus subtilis .

Purification and characterization of the extracellular proteinase of Pseudomonas fluorescens NCDO 2085

Pseudomonas fluorescens NCDO 2085 produced a single heat-stable extracellular proteinase in Na caseinate medium at 20 degrees C and pH 7.0. The proteinase was purified to electrophoretic homogeneity using chromatofocusing, gel filtration and ion-exchange chromatography. The purification procedure resulted in a 158-fold increase in the specific activity and a yield of 3.5% of the original activity. The enzyme is a metalloproteinase containing Zn and Ca, with an isoelectric point at 5.40 +/- 0.05 and a mol. wt of 40 200 +/- 2100. It is heat-stable having D-values at 74 and 140 degrees C of 1.6 and 1.0 min respectively; 40 and 70% of the original activity remained after HTST (74 degrees C/17 s) and ultra high temperature (140 degrees C/4 s) treatments respectively. The amino acid composition of the proteinase was determined and compared with those from other Pseudomonas spp.

Comparative peptide specificity of cell wall, membrane and intracellular peptidases of group N streptococci

Solubilized cell walls of group N streptococci contain two electrophoretically distinct peptidases, one of which hydrolysed trileucine only, while the second hydrolysed a wide range of di- and tripeptides. Neither enzyme possessed leucine aminopeptidase or endopeptidase activity. Four and three peptidases, respectively, were separated in intracellular extracts of Streptococcus lactis subsp. lactis and Strep. lactis subsp. cremoris produced by osmotic lysis of spheroplasts. In contrast with the cell-wall extracts, two of the peptidases had broad specificites, though only one of these hydrolysed trileucine. Purified membranes of Strep. lactis subsp. lactis contained only one electrophoretically distinct peptidase of very narrow specificity. There were small differences between the numbers of peptides hydrolysed by cell wall preparations from milk-grown or broth-grown cells.