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Li S, He H, Zhang Y, Ning X, Ding Z, Zhang L, Li Y, Shi G. Identification of a Novel Lactose-Specific PTS Operon in Bacillus licheniformis and Development of Derivative Artificial Operon Modules. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2023. [PMID: 37927088 DOI: 10.1021/acs.jafc.3c05307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2023]
Abstract
Bacillus licheniformis plays a crucial role as a microbial host in the food industry and shows promising potential as a probiotic for human intestinal regulation. It exhibits a remarkable ability to utilize lactose as its sole carbon source. Despite its significance, the lactose-related metabolic pathway in this strain remains unclear. In this study, we identified a novel lactose-specific operon (lacDCAB) in B. licheniformis, consisting of the lacD gene that encodes a unique 6-phospho-β-galactosidase belonging to the GH4 family, and the lacCAB genes encoding a lactose-specific PTS1 system. Notably, we constructed and assessed an array library of transport and catabolic modules specifically for lactose utilization. Among these modules, PDS-lacD-P2-pts1 demonstrated the highest specific lactose consumption rate of 0.64 g/(L·h·OD), which was 8 times higher than that of the control strain. Furthermore, we developed a dual carbon source transport model based on the PDS-lacD-P2-pts1 assembly module, which highlighted efficient coutilization of glucose/sucrose, lactose/sucrose, lactose/galactose, and lactose/2,3-butanediol. This study provides insight into the lactose-specific metabolic pathway of B. licheniformis and presents a promising strategy for enhancing lactose utilization efficiency and mixed carbon source coutilization.
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Affiliation(s)
- Siyu Li
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
| | - Hehe He
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
| | - Yupeng Zhang
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
| | - Xuewei Ning
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
| | - Zhongyang Ding
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
| | - Liang Zhang
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
| | - Youran Li
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
| | - Guiyang Shi
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China
- National Engineering Research Center for Cereal Fermentation and Food Biomanufacturing, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, People's Republic of China
- Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, People's Republic of China
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Function Trumps Form in Two Sugar Symporters, LacY and vSGLT. Int J Mol Sci 2021; 22:ijms22073572. [PMID: 33808202 PMCID: PMC8037263 DOI: 10.3390/ijms22073572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 03/18/2021] [Accepted: 03/24/2021] [Indexed: 11/21/2022] Open
Abstract
Active transport of sugars into bacteria occurs through symporters driven by ion gradients. LacY is the most well-studied proton sugar symporter, whereas vSGLT is the most characterized sodium sugar symporter. These are members of the major facilitator (MFS) and the amino acid-Polyamine organocation (APS) transporter superfamilies. While there is no structural homology between these transporters, they operate by a similar mechanism. They are nano-machines driven by their respective ion electrochemical potential gradients across the membrane. LacY has 12 transmembrane helices (TMs) organized in two 6-TM bundles, each containing two 3-helix TM repeats. vSGLT has a core structure of 10 TM helices organized in two inverted repeats (TM 1–5 and TM 6–10). In each case, a single sugar is bound in a central cavity and sugar selectivity is determined by hydrogen- and hydrophobic- bonding with side chains in the binding site. In vSGLT, the sodium-binding site is formed through coordination with carbonyl- and hydroxyl-oxygens from neighboring side chains, whereas in LacY the proton (H3O+) site is thought to be a single glutamate residue (Glu325). The remaining challenge for both transporters is to determine how ion electrochemical potential gradients drive uphill sugar transport.
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Di Cera E. Mechanisms of ligand binding. BIOPHYSICS REVIEWS 2020; 1:011303. [PMID: 33313600 PMCID: PMC7714259 DOI: 10.1063/5.0020997] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 09/09/2020] [Indexed: 12/25/2022]
Abstract
Many processes in chemistry and biology involve interactions of a ligand with its molecular target. Interest in the mechanism governing such interactions has dominated theoretical and experimental analysis for over a century. The interpretation of molecular recognition has evolved from a simple rigid body association of the ligand with its target to appreciation of the key role played by conformational transitions. Two conceptually distinct descriptions have had a profound impact on our understanding of mechanisms of ligand binding. The first description, referred to as induced fit, assumes that conformational changes follow the initial binding step to optimize the complex between the ligand and its target. The second description, referred to as conformational selection, assumes that the free target exists in multiple conformations in equilibrium and that the ligand selects the optimal one for binding. Both descriptions can be merged into more complex reaction schemes that better describe the functional repertoire of macromolecular systems. This review deals with basic mechanisms of ligand binding, with special emphasis on induced fit, conformational selection, and their mathematical foundations to provide rigorous context for the analysis and interpretation of experimental data. We show that conformational selection is a surprisingly versatile mechanism that includes induced fit as a mathematical special case and even captures kinetic properties of more complex reaction schemes. These features make conformational selection a dominant mechanism of molecular recognition in biology, consistent with the rich conformational landscape accessible to biological macromolecules being unraveled by structural biology.
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Affiliation(s)
- Enrico Di Cera
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104, USA
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Omeis F, Santos Seica AF, Ermolova N, Kaback HR, Hellwig P. Monoclonal antibody 4B1 influences the pK a of Glu325 in lactose permease (LacY) from Escherichia coli: evidence from SEIRAS. FEBS Lett 2020; 594:3356-3362. [PMID: 32780424 DOI: 10.1002/1873-3468.13907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 08/05/2020] [Accepted: 08/06/2020] [Indexed: 11/11/2022]
Abstract
The monoclonal antibody 4B1 binds to a conformational epitope on the periplasmic side of lactose permease (LacY) of Escherichia coli and inhibits H+ /lactose symport and lactose efflux under nonenergized conditions. At the same time, ligand binding and translocation reactions that do not involve net H+ translocation remain unaffected by 4B1. In this study, surface-enhanced infrared absorption spectroscopy applied to the immobilized LacY was used to study the pH-dependent changes in LacY and to access in situ the effect of the 4B1 antibody on the pKa of Glu325, the primary functional H+ -binding site in LacY. A small shift of the pK value from 10.5 to 9.5 was identified that can be corroborated with the inactivation of LacY upon 4B1 binding.
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Affiliation(s)
- Fatima Omeis
- Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CMC, Université de Strasbourg CNRS, Strasbourg, France.,University of Strasbourg Institute for Advanced Studies (USIAS), Strasbourg, France
| | - Ana Filipa Santos Seica
- Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CMC, Université de Strasbourg CNRS, Strasbourg, France
| | - Natalia Ermolova
- Department of Physiology, University of California, Los Angeles, CA, USA
| | - H Ronald Kaback
- Department of Physiology, University of California, Los Angeles, CA, USA.,Department of Microbiology, Immunology & Molecular Genetics, University of California, Los Angeles, CA, USA.,Molecular Biology Institute, University of California, Los Angeles, CA, USA
| | - Petra Hellwig
- Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CMC, Université de Strasbourg CNRS, Strasbourg, France.,University of Strasbourg Institute for Advanced Studies (USIAS), Strasbourg, France
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The proton electrochemical gradient induces a kinetic asymmetry in the symport cycle of LacY. Proc Natl Acad Sci U S A 2019; 117:977-981. [PMID: 31889006 PMCID: PMC6969543 DOI: 10.1073/pnas.1916563117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protonation and deprotonation of Glu325 with a pKa of 10.5 is required for symport. Moreover, the H+ electrochemical gradient (∆μ∼H+) accelerates deprotonation on the intracellular side with a 50- to 100-fold decrease in the Km. To probe the pK on the cytoplasmic side of the membrane, rates of lactose/H+ efflux were determined from pH 5.0 to 9.0 without or with a membrane potential (ΔΨ, interior positive) in right-side-out membrane vesicles. WT lactose efflux has an apparent pK of ∼7.2 that is unaffected by ΔΨ, mutant E325A is defective, and pH or ΔΨ (interior positive) has no effect. The effect of ΔΨ (interior positive) on the Km for efflux with WT LacY is insignificant relative to the marked effect on influx. LacY catalyzes accumulation of galactosides against a concentration gradient by coupling galactoside and H+ transport (i.e., symport). While alternating access of sugar- and H+-binding sites to either side of the membrane is driven by binding and dissociation of sugar, the electrochemical H+ gradient (∆μ∼H+) functions kinetically by decreasing the Km for influx 50- to 100-fold with no change in Kd. The affinity of protonated LacY for sugar has an apparent pK (pKapp) of ∼10.5, due specifically to the pKa of Glu325, a residue that plays an irreplaceable role in coupling. In this study, rates of lactose/H+ efflux were measured from pH 5.0 to 9.0 in the absence or presence of a membrane potential (ΔΨ, interior positive), and the effect of the imposed ΔΨ on the kinetics of efflux was also studied in right-side-out membrane vesicles. The findings reveal that ∆μ∼H+ induces an asymmetry in the transport cycle based on the following observations: 1) the efflux rate of WT LacY exhibits a pKapp of ∼7.2 that is unaffected by the imposed ΔΨ; 2) ΔΨ increases the rate of efflux at all tested pH values, but enhancement is almost 2 orders of magnitude less than observed for influx; 3) mutant Glu325 ˗ Ala does little or no efflux in the absence or presence of ΔΨ, and ambient pH has no effect; and 4) the effect of ΔΨ (interior positive) on the Km for efflux is almost insignificant relative to the 50- to 100-fold decrease in the Km for influx driven by ΔΨ (interior negative).
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Abstract
The lactose permease of Escherichia coli (LacY) utilizes an alternating access symport mechanism with multiple conformational intermediates, but only inward (cytoplasmic)- or outward (periplasmic)-open structures have been characterized by X-ray crystallography. It is demonstrated here with sugar-binding studies that cross-linking paired-Cys replacements across the closed cytoplasmic cavity stabilize an occluded conformer with an inaccessible sugar-binding site. In addition, a nanobody (Nb) that stabilizes a periplasmic-open conformer with an easily accessible sugar-binding site in WT LacY fails to cause the cytoplasmic cross-linked mutants to become accessible to galactoside, showing that the periplasmic cavity is closed. These results are consistent with tight association of the periplasmic ends in two pairs of helices containing clusters of small residues in the packing interface between N- and C-terminal six-helix bundles of the symporter. However, after reduction of the disulfide bond, the Nb markedly increases the rate of galactoside binding, indicating unrestricted access to the Nb epitope and the galactoside-binding site from the periplasm. The findings indicate that the cross-linked cytoplasmic double-Cys mutants resemble an occluded apo-intermediate in the transport cycle.
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Oversized galactosides as a probe for conformational dynamics in LacY. Proc Natl Acad Sci U S A 2018; 115:4146-4151. [PMID: 29602806 DOI: 10.1073/pnas.1800706115] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Binding kinetics of α-galactopyranoside homologs with fluorescent aglycones of different sizes and shapes were determined with the lactose permease (LacY) of Escherichia coli by FRET from Trp151 in the binding site of LacY to the fluorophores. Fast binding was observed with LacY stabilized in an outward-open conformation (kon = 4-20 μM-1·s-1), indicating unobstructed access to the binding site even for ligands that are much larger than lactose. Dissociation rate constants (koff) increase with the size of the aglycone so that Kd values also increase but remain in the micromolar range for each homolog. Phe27 (helix I) forms an apparent constriction in the pathway for sugar by protruding into the periplasmic cavity. However, replacement of Phe27 with a bulkier Trp does not create an obstacle in the pathway even for large ligands, since binding kinetics remain unchanged. High accessibility of the binding site is also observed in a LacY/nanobody complex with partially blocked periplasmic opening. Remarkably, E. coli expressing WT LacY catalyzes transport of α- or β-galactopyranosides with oversized aglycones such as bodipy or Aldol518, which may require an extra space within the occluded intermediate. The results confirm that LacY specificity is strictly directed toward the galactopyranoside ring and also clearly indicate that the opening on the periplasmic side is sufficiently wide to accommodate the large galactoside derivatives tested here. We conclude that the actual pathway for the substrate entering from the periplasmic side is wider than the pore diameter calculated in the periplasmic-open X-ray structures.
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Abstract
Conformational selection (CS) and induced fit (IF) are two widely used interpretations of binding of a ligand to biological macromolecules. Both mechanisms envision a two-step reaction in which a conformational transition either precedes (CS) or follows (IF) the binding step. Under pseudo-first-order conditions where the ligand is in excess compared to the macromolecule, both mechanisms produce two relaxations. A fast one eventually increases linearly with ligand concentration and reflects the binding interaction. A slow one saturates to a constant value after decreasing or increasing hyperbolically with ligand concentration. This relaxation is the one most often accessible to experimental measurements and is potentially diagnostic of the mechanism involved. A relaxation that decreases unequivocally identifies CS, but a hyperbolic increase is compatible with both CS and IF. The potential ambiguity between the two mechanisms is more than qualitative. Here we show that the entire kinetic repertoire of IF is nothing but a mathematical special case of CS as revealed by a simple transformation of the rate constants, which emphasizes the need for independent support of either mechanism from additional experimental evidence. We discuss a simple strategy for distinguishing between IF and CS under the most common conditions encountered in practice, i.e., when the ligand is in excess compared to the macromolecule and a single relaxation is accessible to experimental measurements.
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Affiliation(s)
- Pradipta Chakraborty
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine , St. Louis, Missouri 63104, United States
| | - Enrico Di Cera
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine , St. Louis, Missouri 63104, United States
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