The Proteolytic System of Lactic Acid Bacteria

lactis strains isolated from dairy products are characterized by a high number of amino acid auxotrophies and the ability to utilize milk proteins as an amino acid source. These properties are common to dairy strains even from distant geographic locations in Asia, Europe, North America, and 

New Zealand (Rademaker et al. 2007 Kelly et al. 2010). The use of enviromnental proteins as an amino acid source in LAB explains the importance of their proteolytic system. LAB depend on this system to obtain the essential amino acids that are then used as precursors for not only peptides and proteins but also for many otha-biomolecules. Amino acids are the precursors of aromatic compounds, which are important to the final flavor of food products. Proteolytic activity also generates other molecules, such as bioactive peptides, that have functions related to the probiotic properties of LAB. 

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Kok, J. (1990). Genetics of the proteolytic system of lactic acid bacteria. FEMS Microbiol. Rev. 87, 15-41. 

Kunji, E. R., Mierau, L, Hagting, A., Pooknan, B., Konings, W. N. (1996). The proteolytic systems of lactic acid bacteria. Antonie Van Leeuwenhoek, 70, 187-221. 

Kok J, DeVos JM (1994) The proteolytic system of lactic acid bacteria. In Gasson MJ, DeVos WM (eds) Genetics and biotechnology of lactic add bacteria. Blackie Academic/Professional Publishers, London, New York, pp 169-210... 

Figure 1.3. Diagram of the proteolytic systems of lactic acid bacteria, (a) Extracellular components PrtP, cell-envelope proteinase PrtM, proteinase maduration protein Opp, oligopetide permease DtpT, the ion linked trasnsporter for di-and tripeptides and Opt, the ABC transporter for peptides, (b) Intracelullar components pool of about 20-25 peptidases, including general (PepN, PepC) and specific (PepX, PepQ) peptidases, and amino acid catabolic enzymes (carboxylases, aminotransferases, etc.).

Liu, M., Bayjanov, J.R., Renckens, B., et al. (2010) The proteolytic system of lactic acid bacteria revisited a genomic comparison. BMC Genomics 11, 36. 

This is due to the nature of the sourdough system where the effects of acidification and the endogenous microbial and cereal proteases all contribute to a complex set of dynamics. It is further complicated by the fact that there may be divergence between studies in terms of the particular lactoba-cilli used given that proteolytic activity is strain dependent. The enhanced proteolysis seen during sourdough fermentation has been attributed to both the proteolytic activity of lactic acid bacteria and that of cereal proteases. 

Poolman B, Kunji E, Hagting A, Juillard V, Konings W (1995) The proteolytic pathway of Lactococcus lactis. J Appl Bacteriol 79 65S-75S Pritchard GG, Coolbear T (1993) The physiology and biochemistry of the proteolytic system in lactic acid bacteria. FEMS Microbiol Rev 12 179-206 Rafter JJ (1995) The role oflactic acid bacteria in colon cancer prevention. Scand J Gastroenterol 30 497-502... 

Although lactic acid bacteria (LAB) are weakly proteolytic they do possess a proteinase and a wide range of peptidases which are principally responsible for the formation of small peptides and amino acids in cheese. The genus most widely used as a cheese starter is Lactococcus, the proteolytic system of which has been studied thoroughly at the molecular, biochemical, and genetic levels. The proteolytic system of Lactobacillus spp. is less well characterized than that of Lactococcus, but the systems of both genera appear to be generally similar. 

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