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

• Published in: Molecular microbiology Vol. 105; no. 1; pp. 25 - 45
• Main Authors: Homburg, Constanze, Bommer, Martin, Wuttge, Steven, Hobe, Carolin, Beck, Sebastian, Dobbek, Holger, Deutscher, Josef, Licht, Anke, Schneider, Erwin
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.07.2017; Wiley
• Subjects: Adenosine triphosphatase; Adenosine triphosphate; ATP-Binding Cassette Transporters - metabolism; Bacteria; Bacterial Proteins - metabolism; Binding; Biochemistry; Carbohydrates; Carbon; Carbon sources; Catabolite repression; Crosslinking; Crystal structure; DNA-Binding Proteins - metabolism; E coli; Firmicutes - metabolism; Glucose; Homology; Hydrolysis; Lactobacilli; Lactobacillus casei; Lactobacillus casei - genetics; Lactobacillus casei - metabolism; Life Sciences; Maltodextrin; Maltose; Maltose - analogs & derivatives; Maltose - metabolism; Maltotetraose; Mode of action; Mutagenesis; Mutation; Phosphoenolpyruvate Sugar Phosphotransferase System - metabolism; Phosphorylation; Phosphotransferase; Phosphotransferases - metabolism; Proteins; Proximity; Repressor Proteins - metabolism; Serine; Signal Transduction; Substrate inhibition; Sugar; Transport
• ISSN: 0950-382X; 1365-2958; 1365-2958
• DOI: 10.1111/mmi.13680

Summary 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‐MalF1G1K12) 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. A maltodextrin ABC transporter (MalE1‐MalF1G1K12) is subject to inducer exclusion in Lactobacillus casei BL23 when a favored carbon source such as glucose is available. The PTS component HPr phosphorylated at Ser‐46 inhibits the ATPase activity of the purified transporter in lipid environment by targeting the nucleotide‐binding subunits, MalK12, in proximity to the ATP‐binding (Walker A) motif. However, P‐Ser46‐HPr does not prevent nucleotide binding per se.