Inducer exclusion in Firmicutes: insights into the regulation of a carbohydrate ATP binding cassette transporter from Lactobacillus casei BL23 by the signal transducing protein P‐Ser46‐HPr

Abstract

Catabolite repression is a mechanism that enables bacteria to control carbon utilization. As part of this global regulatory network, components of the phosphoenolpyruvate:carbohydrate phosphotransferase system inhibit the uptake of less favorable sugars when a preferred carbon source such as glucose is available. This process is termed inducer exclusion. In bacteria belonging to the phylum Firmicutes, HPr, phosphorylated at serine 46 (P-Ser46-HPr) is the key player but its mode of action is elusive. To address this question at the level of purified protein components, we have chosen a homolog of the Escherichia coli maltose/maltodextrin ATP-binding cassette transporter from Lactobacillus casei (MalE1-MalF1G1K1 ) as a model system. We show that the solute binding protein, MalE1, binds linear and cyclic maltodextrins but not maltose. Crystal structures of MalE1 complexed with these sugars provide a clue why maltose is not a substrate. P-Ser46-HPr inhibited MalE1/maltotetraose-stimulated ATPase activity of the transporter incorporated in proteoliposomes. Furthermore, cross-linking experiments revealed that P-Ser46-HPr contacts the nucleotide-binding subunit, MalK1, in proximity to the Walker A motif. However, P-Ser46-HPr did not block binding of ATP to MalK1. Together, our findings provide first biochemical evidence that P-Ser-HPr arrests the transport cycle by preventing ATP hydrolysis at the MalK1 subunits of the transporter.

Enterococcus faecalis MalR acts as a repressor of the maltose operons and additionally mediates their catabolite repression via direct interaction with seryl‐phosphorylated‐HPr

“…In oligotrophic milieu and under harsh competition, optimisation of carbohydrate utilisation can be essential for survival. The central sensor of CCR, P‐Ser‐HPr, is known to play a major role in metabolic regulation in Firmicutes (Deutscher, ) by functioning as a corepressor of the global regulator CcpA or by directly inhibiting non‐PTS transporters (Dossonnet et al, ; Homburg et al, ; Monedero, Yebra, Poncet, & Deutscher, ; Viana et al, ; Ye, Minarcik, & Saier, ). P‐Ser‐HPr was also shown to interact in vitro with the B. subtilis LacI/GalR‐type transcriptional regulator RbsR (Müller, Horstmann, Hillen, & Sticht, ), but no physiological function was reported for the complex.…”

“…In oligotrophic milieu and under harsh competition, optimisation of carbohydrate utilisation can be essential for survival. The central sensor of CCR, P-Ser-HPr, is known to play a major role in metabolic regulation in Firmicutes (Deutscher, 2008) by functioning as a corepressor of the global regulator CcpA or by directly inhibiting non-PTS transporters Homburg et al, 2017;Monedero, Yebra, Poncet, & Deutscher, 2008;Viana et al, 2000;Ye, Minarcik, & Saier, 1996).…”

Enzymes Required for Maltodextrin Catabolism in Enterococcus faecalis Exhibit Novel Activities

“…The slow growth on ␣-cyclodextrin disappeared when mmdH was inactivated (data not shown). Interestingly, ␣-and ␤-cyclodextrins bind with high affinity to the maltodextrin binding protein of Lactobacillus casei and induce the closed active conformation (16). The slow growth of E. faecalis on ␣-cyclodextrin might therefore be due to slow utilization of the cyclic compound, but a slight contamination with linear maltodextrins cannot be excluded.…”

“…Maltooligosaccharide utilization in Firmicutes is also subjected to inducer exclusion (29). While in enterobacteria, EIIA Glc interacts with and inhibits MalK, P-Ser46-HPr has recently been reported to interact with MalK1 of L. casei (16), and a similar mechanism is probably operative in E. faecalis. P-Ser46-HPr-mediated catabolite repression takes about 30 min to become effective, whereas P-Ser46-HPr-requiring inducer exclusion leads to an almost instant stop of maltodextrin uptake (29) and hence formation of the inducer.…”

Photoinactivation of the <b><i>Staphylococcus aureus</i></b> Lactose-Specific EIICB Phosphotransferase Component with <b><i>p</i></b>-azidophenyl-β-D-Galactoside and Phosphorylation of the Covalently Bound Substrate

“…In Firmicutes, MalK activity is inhibited by P-Ser-HPr [Homburg et al, 2017], which is formed by reversible phosphorylation by HPr kinase/phosphorylase [Deutscher et al, , 2014. An interface, which usually includes the phosphorylation site of the PTS components, is used for their interaction with non-PTS target proteins.…”