Regulation of branched-chain amino acid biosynthesis by α-acetolactate decarboxylase inStreptococcus thermophilus

Abstract

Aims: To demonstrate the presence of an active a-acetolactate decarboxylase in Streptococcus thermophilus and to investigate its physiological function. Methods and Results: Streptococcus thermophilus CNRZ385 contains a gene encoding an a-acetolactate decarboxylase. Comparison of the production of a-acetolactate and its decarboxylation products, by the parent strain and an a-acetolactate decarboxylase-deficient mutant, demonstrated the presence of a control of the pool of a-acetolactate by valine, leucine and isoleucine. This control occurs via an allosteric activation of the a-acetolactate decarboxylase. Cell-free extracts of S. thermophilus were not able to decarboxylate the isoleucine precursor a-acetohydroxybutyrate. Conclusions: These results strongly suggest that one of the physiological functions of the a-acetolactate decarboxylase in S. thermophilus is to regulate leucine and valine biosynthesis by diverting the flux of a-acetolactate towards acetoin when the branched-chain amino acids are present at a high concentration. Significance and Impact of the Study: Regulation of branched-chain amino acid biosynthesis by a-acetolactate decarboxylase may occur in several other micro-organisms and explain some of their growth properties.

A thermophilic cell-free cascade enzymatic reaction for acetoin synthesis from pyruvate

“…subtilis , the gene alsS encoding cALS and the gene alsD encoding ALDC belong to a single operon, which is controlled by the AlsR regulator 11 . The activation of ALDC by BCAAs has already been observed in microorganisms 12 . However, the ALDC from L .…”

Complete Sequences of Four Plasmids ofLactococcus lactissubsp.cremorisSK11 Reveal Extensive Adaptation to the Dairy Environment

“…A second, chromosomally encoded AldC of strain SK11 has 98% identity to a second chromosomally encoded AldC of L. lactis IL1403. This enzyme converts ␣-acetolactate to acetoin and has potential significance in the dairy environment in the regulation of branched-chain amino acid biosynthesis (50). Alternatively, since acetoin can be further reduced to butanediol, the activity of ␣-acetolactate decarboxylase may contribute to the formation of an additional electron sink.…”

Streptococcus thermophilus strains: Multifunctional lactic acid bacteria

“…Genomic analysis of S. thermophilus has shown that it maintained the capacity to use caseins and to synthesize several amino acids throughout evolution, and both aspects reveal adaptation of this species to milk. Single and multiple amino acid omission analysis showed that the number and type of essential amino acids required for growth is strain-dependent (Letort & Juillard, 2001), with some S. thermophilus strains exhibiting no absolute amino acid requirement (Monnet et al, 2003).…”