Characterization of the pattern of _s1- and -caseins breakdown and release of a bioactive peptide by a cell-envelope proteinase from Lactobacillus delbrueckii subsp. lactis CRL 581

Centro de Referencia para Lactobacilos (CERELA-CONICET), 4000 San Miguel de Tucumán, Argentina; Istituto di Scienze dell'Alimentazione del CNR, Via Roma 52, I83-100, Avellino, Italy

^* To whom correspondence should be addressed. Email: ehebert{at}cerela.org.ar.

	Abstract

The cell envelope-associated proteinase (CEP) of lactobacilli has a key role for bacterial nutrition and contributes to the development of the organoleptic properties of fermented milk products as well as it can release bioactive health-beneficial peptides from milk proteins. The influence of the peptide supply, carbohydrate source and osmolites on the CEP activity of the cheese starter Lactobacillus delbrueckii subsp. lactis CRL 581 was investigated. CEP activity levels were controlled by the peptide content of the growth medium. The maximum activity was observed in a basal minimal defined medium whereas in the presence of Casitone, Casamino acids or yeast extract the synthesis of CEP was inhibited 99-, 70- and 68-fold, respectively. The addition of specific di- or tripeptides containing branched-chain amino acids, such as leucylleucine, prolylleucine, leucylglycylglycin or leucylproline to the growth medium negatively affected CEP activity whereas dipeptides without branched-chain amino acids had no effect on the enzyme production. The carbon source and osmolites did no affect CEP activity. The CEP of L. delbrueckii subsp. lactis CRL 581 exhibited a mixed type CEP_I/III variant caseinolytic specificity. Mass spectrometric screening of the main peptide peaks isolated by RP-HPLC allowed identification of 33- and 32-peptides in the _s1- and -casein hydrolysates, respectively. By characterizing the peptide sequence in these hydrolysates, a pattern of _s1- and -caseins breakdown was defined, being this the first report for a CEP of Lactobacillus delbrueckii subsp. lactis. In this pattern a series of potentially bioactive peptides (antihypertensive and phosphopeptides), which are encrypted within the precursor protein, could be visualized.