GO:0008745 N-acetylmuramoyl-L-alanine amidase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0008745 describes the enzymatic activity that hydrolyzes the bond between N-acetylmuramoyl residues and L-amino acid residues in bacterial cell-wall glycopeptides, a key step in peptidoglycan turnover and bacterial cell lysis.
• This activity is found across diverse organisms, from bacteria such as Escherichia coli, Bacillus amyloliquefaciens and Latilactobacillus sakei to mammals including humans, where it is carried out by peptidoglycan recognition proteins (PGRPs).
• In bacteria, the amidase contributes to cell wall remodeling, cell separation and autolysis, and its manipulation can enhance heterologous protein production.
• In mammals, PGRP-L and other PGRP family members with amidase activity participate in innate immune recognition and degradation of bacterial peptidoglycan.
• The enzyme has been purified and characterized from human serum, indicating a role in systemic antibacterial defense.
• Research on this activity spans microbiology, immunology and biotechnology, with methods including enzymatic assays, structural biology, knockout models and heterologous expression.
Description
N-acetylmuramoyl-L-alanine amidase activity (GO:0008745) is a molecular function that catalyzes the hydrolysis of the amide bond linking N-acetylmuramoyl residues to L-amino acid residues within bacterial cell-wall glycopeptides. This activity is central to peptidoglycan metabolism, the dynamic mesh that surrounds bacterial cells and maintains their shape and integrity. Because peptidoglycan is essential for bacterial survival, enzymes that cleave it are attractive targets for antibacterial strategies and are also key players in host-pathogen interactions. The amidase activity has been identified in a wide range of organisms, including Gram-negative and Gram-positive bacteria, bacteriophages, and mammals. In bacteria, it contributes to cell wall turnover, cell division and autolysis, and its deletion or overexpression can affect cell lysis and protein production yields. In mammals, peptidoglycan recognition proteins (PGRPs) such as PGRP-L exhibit this amidase activity and function in innate immunity by degrading bacterial peptidoglycan. The presence of a serum amidase in humans further underscores its physiological relevance in systemic defense. For researchers, GO:0008745 represents a convergence point for microbiology, immunology and biotechnology, offering opportunities to study bacterial physiology, host-microbe interactions and to engineer improved microbial strains.
N-acetylmuramoyl-L-alanine amidase activity At A Glance
| GO ID | GO:0008745 |
|---|---|
| GO term | N-acetylmuramoyl-L-alanine amidase activity |
| Ontology | molecular_function |
| Synonym | acetylmuramoyl-alanine amidase activity; acetylmuramyl-alanine amidase activity; acetylmuramyl-L-alanine amidase activity; N-acetylmuramic acid L-alanine amidase activity; N-acetylmuramoyl-L-alanine amidase type I; N-acetylmuramoyl-L-alanine amidase type II; N-acetylmuramylalanine amidase activity; N-acetylmuramyl-L-alanine amidase activity; N-acylmuramyl-L-alanine amidase activity |
| Major function | Hydrolysis of the link between N-acetylmuramoyl residues and L-amino acid residues in bacterial cell-wall glycopeptides |
| EC number | 3.5.1.28 |
| Found in | Bacteria (e.g., Escherichia coli, Bacillus amyloliquefaciens, Latilactobacillus sakei), mammals (e.g., human serum, PGRP-L) |
| Substrates | Peptidoglycan, bacterial cell-wall glycopeptides |
| Related proteins | Peptidoglycan recognition proteins (PGRPs), bacterial autolysins |
What Is GO:0008745?
According to the Gene Ontology, GO:0008745 (N-acetylmuramoyl-L-alanine amidase activity) is defined as the catalysis of the hydrolysis of the link between N-acetylmuramoyl residues and L-amino acid residues in certain bacterial cell-wall glycopeptides. In simpler terms, it is an enzyme activity that cuts the amide bond connecting the sugar backbone of peptidoglycan to the peptide chain, thereby breaking down the bacterial cell wall. This activity is also known by several synonyms, including acetylmuramoyl-alanine amidase activity, N-acetylmuramyl-L-alanine amidase activity, and N-acetylmuramoyl-L-alanine amidase type I and type II.
Why Is N-acetylmuramoyl-L-alanine amidase activity Important in Cell Biology?
GO:0008745 is important because it governs a critical step in bacterial cell wall metabolism and host defense. In bacteria, the amidase activity is involved in cell wall turnover, cell separation and autolysis, processes that are essential for growth and division. Modulating this activity can influence cell lysis and heterologous protein production, making it a target for biotechnological applications. In mammals, PGRP-L and other PGRPs with amidase activity are part of the innate immune system, where they recognize and degrade bacterial peptidoglycan, thereby controlling bacterial infections and modulating inflammation. The presence of an amidase in human serum further highlights its role in systemic antibacterial defense. Understanding this activity can inform the development of novel antibacterial agents, improve industrial fermentation processes, and elucidate mechanisms of immune recognition.
• Essential for bacterial cell wall turnover and cell division.
• Contributes to autolysis and cell lysis in bacteria, affecting protein production.
• Involved in innate immune recognition of bacteria by PGRPs.
• Human serum amidase provides systemic antibacterial defense.
• Potential target for new antibacterial drugs.
• Biotechnological tool for improving heterologous protein production.
• Model for studying peptidoglycan degradation and recycling.
• Relevant to host-microbe interactions and inflammatory diseases.
• Enables engineering of probiotic strains like Latilactobacillus sakei.
• Provides insights into enzyme evolution and catalytic mechanisms.
Molecular Mechanism of N-acetylmuramoyl-L-alanine amidase activity
Substrate Recognition and Binding
In simple terms: The enzyme first grabs onto the bacterial cell wall by recognizing specific sugar and peptide features.
N-acetylmuramoyl-L-alanine amidases specifically recognize the glycan backbone of peptidoglycan, particularly N-acetylmuramoyl residues, and the adjacent L-alanine residue. The enzyme binds to the bacterial cell wall glycopeptides through a substrate-binding cleft that accommodates the muramoyl moiety and the peptide stem. In mammalian PGRP-L, the binding is mediated by a conserved peptidoglycan-binding groove that confers specificity for muramyl peptides. This initial recognition step is crucial for the enzyme's ability to discriminate between different peptidoglycan types and to avoid attacking host glycans.
Catalytic Hydrolysis
In simple terms: Once bound, the enzyme cuts the bond between the sugar and the amino acid, breaking the cell wall.
The catalytic mechanism involves the hydrolysis of the amide bond between the N-acetylmuramoyl residue and the L-alanine residue. This reaction is typically mediated by a zinc ion in the active site of many amidases, including PGRP-L, where a conserved zinc-binding motif (HExxH) coordinates the metal ion that activates a water molecule for nucleophilic attack. In bacterial amidases such as those from Escherichia coli, the catalytic residues and metal dependence have been characterized, and the reaction proceeds through a general acid-base mechanism. The hydrolysis products are free N-acetylmuramoyl peptides and L-amino acids, which can be further degraded or recycled.
Cofactors and Metal Dependence
In simple terms: Many of these enzymes need a metal helper, usually zinc, to work properly.
Zinc is a common cofactor for N-acetylmuramoyl-L-alanine amidases. For human PGRP-L, zinc is essential for enzymatic activity, and mutation of the zinc-binding residues abolishes amidase function. Similarly, the Escherichia coli amidase has been shown to require metal ions for optimal activity, although the exact metal may vary. The phospholipid environment can also influence activity, as demonstrated for the amidase in phospholipidic environments, suggesting membrane interactions may modulate catalysis. These cofactors and environmental factors are critical for regulating the enzyme's function in vivo.
Regulation and Physiological Roles
In simple terms: The enzyme's activity is controlled by the cell and can change depending on growth conditions or immune signals.
In bacteria, the expression and activity of N-acetylmuramoyl-L-alanine amidases are tightly regulated in response to growth phase and cell wall stress. For example, in Escherichia coli, the amidase plays a role in cell separation and autolysis, and its activity is modulated by other cell wall hydrolases. In Bacillus amyloliquefaciens, manipulation of the amidase gene affects cell lysis and heterologous protein production, indicating that its regulation is important for industrial processes. In mammals, PGRP-L expression is induced by bacterial challenge, and its amidase activity contributes to the degradation of peptidoglycan, thereby dampening immune responses. The human serum amidase may also be regulated by systemic factors, though details remain to be fully elucidated.
Structural Features and Domain Organization
In simple terms: The enzyme has different parts that help it bind to the cell wall and cut it.
N-acetylmuramoyl-L-alanine amidases typically possess a catalytic domain and one or more cell wall-binding domains, such as LysM domains. In Latilactobacillus sakei, deletion of the LysM domain altered the antimicrobial spectrum, suggesting that these domains modulate substrate specificity and activity. Mammalian PGRPs have a single PGRP domain that carries the amidase activity, and some, like PGRP-L, are secreted or membrane-bound. The structural organization determines the enzyme's localization and access to peptidoglycan, which is critical for its function in different environments.
Key Genes Involved in GO:0008745 N-acetylmuramoyl-L-alanine amidase activity
The following genes and proteins are directly associated with N-acetylmuramoyl-L-alanine amidase activity, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ampD (E. coli) | Cytoplasmic amidase involved in peptidoglycan recycling | Model for studying cell wall turnover and antibiotic resistance |
| PGRP-L (human) | Secreted amidase that degrades bacterial peptidoglycan | Innate immunity and antibacterial defense |
| PGRP-S (human) | Short PGRP with amidase activity | Peptidoglycan recognition and immune modulation |
| PGLYRP2 (human) | Peptidoglycan recognition protein L, serum amidase | Systemic antibacterial defense |
| lytA (phage) | Phage endolysin with amidase activity | Bacterial lysis and phage therapy |
| cwlD (Bacillus) | Amidase involved in spore cortex hydrolysis | Spore germination and cell wall metabolism |
| sakA (Latilactobacillus sakei) | Amidase with antibacterial activity | Probiotic and antimicrobial applications |
| amiA (E. coli) | Amidase involved in cell separation | Cell division and autolysis |
| amiB (E. coli) | Amidase with redundant functions | Cell wall remodeling |
| amiC (E. coli) | Amidase required for cell separation | Cell division and biofilm formation |
| PGRP-Iα (human) | Peptidoglycan recognition protein with amidase activity | Innate immunity |
| PGRP-Iβ (human) | Peptidoglycan recognition protein with amidase activity | Innate immunity |
| PGRP-S (mouse) | Amidase involved in antibacterial defense | Mouse models of infection |
| PGRP-L (mouse) | Amidase that modulates inflammation | Host-microbe interactions |
| LysM domain proteins | Cell wall binding modules | Engineering antimicrobial spectrum |
| Zinc-binding amidases | Catalytic domain with zinc | Enzyme mechanism and inhibitor design |
| Serum amidase (human) | Circulating amidase activity | Biomarker and defense |
How Is N-acetylmuramoyl-L-alanine amidase activity Regulated?
The activity of N-acetylmuramoyl-L-alanine amidases is regulated at multiple levels. In bacteria, expression is often controlled by cell wall stress response pathways and growth phase, ensuring that autolysis occurs at the appropriate time. For example, in Escherichia coli, the amidases AmiA, AmiB and AmiC are regulated by the NlpI-Prc complex and other factors that control cell separation. In Bacillus amyloliquefaciens, the amidase gene is expressed during stationary phase and affects cell lysis and heterologous protein production. In mammals, PGRP-L expression is induced by bacterial components through NF-κB signaling, and its amidase activity is regulated by zinc availability and post-translational modifications. The phospholipid environment can also modulate amidase activity, as shown for the enzyme in phospholipidic environments. Additionally, the human serum amidase may be regulated by systemic inflammatory mediators, though further studies are needed.
N-acetylmuramoyl-L-alanine amidase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PGRP-L | Inflammatory bowel disease, sepsis | PGLYRP2 knockout mouse |
| PGRP-S | Bacterial infections | PGLYRP1 knockout mouse |
| ampD | Antibiotic resistance | E. coli ampD mutant |
| lytA | Phage therapy | Phage lysin engineering |
| sakA | Foodborne pathogens | Lactobacillus expression system |
Bacterial Infections and Innate Immunity
N-acetylmuramoyl-L-alanine amidases play a dual role in bacterial infections. In pathogens, these enzymes contribute to cell wall remodeling and virulence, while in the host, PGRPs with amidase activity degrade peptidoglycan to control bacterial burden and modulate inflammation. Deficiencies in PGRP-L have been associated with increased susceptibility to bacterial infections and exacerbated inflammatory responses. The human serum amidase may also contribute to systemic clearance of bacterial components. Understanding these interactions could lead to new therapies for sepsis and chronic infections.
Inflammatory Diseases
Peptidoglycan fragments are potent inflammatory stimuli, and their degradation by amidases can dampen inflammation. PGRP-L, which possesses amidase activity, has been shown to reduce inflammation in models of colitis and arthritis by degrading peptidoglycan. Conversely, dysregulated amidase activity may contribute to chronic inflammatory conditions. The balance between peptidoglycan recognition and degradation is critical for maintaining immune homeostasis.
Biotechnological and Industrial Applications
In industrial microbiology, modulating amidase activity can enhance heterologous protein production by controlling cell lysis. In Bacillus amyloliquefaciens, deletion of the amidase gene reduced cell lysis and improved protein yields. Similarly, the amidase from Latilactobacillus sakei has been explored for its antimicrobial properties, with potential applications in food preservation and probiotics. These biotechnological applications highlight the importance of understanding amidase regulation.
From N-acetylmuramoyl-L-alanine amidase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does the amidase gene affect bacterial cell lysis? | Knockout of amidase gene in Bacillus amyloliquefaciens |
| What is the role of PGRP-L in innate immunity? | PGLYRP2 knockout mouse |
| How does the LysM domain affect antimicrobial spectrum? | LysM domain deletion in Latilactobacillus sakei amidase |
| What is the catalytic mechanism of human PGRP-S? | Point mutations in zinc-binding residues |
| Can amidase activity be used to improve protein production? | Overexpression of amidase in E. coli |
| What is the physiological function of E. coli amidase? | amiA, amiB, amiC triple mutant |
How to Study the N-acetylmuramoyl-L-alanine amidase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Colorimetric assay | Release of free amino groups | Quantifying amidase activity in bacterial lysates |
| Zymogram | Hydrolysis of peptidoglycan in gels | Detecting amidase activity in complex mixtures |
| Gene knockout | Loss of gene function | Studying physiological roles in bacteria |
| X-ray crystallography | Three-dimensional structure | Understanding catalytic mechanism |
| Isothermal titration calorimetry | Binding affinity | Characterizing substrate binding |
| Western blot | Protein expression levels | Validating knockout or overexpression |
| qRT-PCR | mRNA expression | Measuring gene regulation |
| Mass spectrometry | Peptidoglycan fragments | Identifying hydrolysis products |
Enzymatic Activity Assays
The most direct way to study N-acetylmuramoyl-L-alanine amidase activity is through enzymatic assays using peptidoglycan or synthetic substrates. These assays measure the release of free amino groups or the hydrolysis of specific bonds, often using colorimetric or fluorogenic substrates. For example, the amidase activity of PGRP-L can be measured using muramyl dipeptide derivatives. Zymogram assays with peptidoglycan-containing gels can also detect amidase activity after gel electrophoresis.
Genetic Knockouts and Complementation
Genetic approaches, such as gene knockouts and complementation, are powerful for studying the physiological roles of amidases. In Escherichia coli, deletion of amiA, amiB and amiC results in cell separation defects, which can be rescued by expressing the genes from plasmids. In Bacillus amyloliquefaciens, knockout of the amidase gene reduced cell lysis and increased heterologous protein production. These models help establish causality between amidase activity and cellular phenotypes.
Structural and Biophysical Methods
Structural biology techniques, including X-ray crystallography and NMR, have been used to determine the three-dimensional structures of amidases and their complexes with substrates. For human PGRP-L, the crystal structure revealed a zinc-binding site and a peptidoglycan-binding groove. Biophysical methods such as isothermal titration calorimetry can measure substrate binding affinity. These methods provide insights into the catalytic mechanism and can guide inhibitor design.
Expression and Purification
Recombinant expression and purification of amidases are essential for biochemical and structural studies. Bacterial amidases are often expressed in E. coli and purified using affinity tags. Mammalian PGRPs can be expressed in insect or mammalian cells to ensure proper folding and post-translational modifications. The human serum amidase has been purified from serum using chromatographic techniques. These purified enzymes are used for activity assays and crystallization.
How CRISPR Can Be Used to Study GO:0008745 N-acetylmuramoyl-L-alanine amidase activity
Knockout
CRISPR-Cas9 knockout of amidase genes can be used to study their essentiality and physiological roles. For example, knocking out the amidase gene in Bacillus amyloliquefaciens revealed its role in cell lysis and heterologous protein production. In Escherichia coli, CRISPR knockout of amiA, amiB and amiC can recapitulate the cell separation defects observed with traditional mutants. These models are valuable for understanding bacterial cell wall metabolism and for engineering strains with improved traits.
Point Mutation
CRISPR-mediated point mutations can be introduced into catalytic residues of amidases to dissect their enzymatic mechanism. For human PGRP-L, mutation of the zinc-binding histidines abolishes amidase activity, confirming their essential role. Similarly, point mutations in the catalytic domain of bacterial amidases can reveal key residues for substrate binding and catalysis. These precise edits are crucial for structure-function studies.
Knock-in
Knock-in of epitope tags or fluorescent proteins into endogenous amidase genes allows for real-time tracking of protein localization and expression. For example, tagging the E. coli amidase with GFP can reveal its localization during cell division. In mammalian cells, knock-in of a tag into PGLYRP2 can facilitate studies of secretion and trafficking. These models are useful for imaging and proteomic applications.
Overexpression
CRISPR activation (CRISPRa) or plasmid-based overexpression can be used to increase amidase levels and study its effects. Overexpression of the amidase in E. coli can lead to increased autolysis, which can be harnessed for protein release. In Bacillus amyloliquefaciens, overexpression of the amidase increased cell lysis and reduced protein production, highlighting the need for tight regulation. Overexpression models are also useful for producing large amounts of enzyme for structural studies.
How EDITGENE Supports N-acetylmuramoyl-L-alanine amidase activity Research
Researchers studying N-acetylmuramoyl-L-alanine amidase activity-related genes often need to determine whether a candidate gene is causally involved in bacterial cell wall metabolism, host immunity, or biotechnological traits. Establishing causality requires precise genetic manipulation, such as knockout, point mutation, knock-in, or overexpression, followed by functional assays. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate this research, from cell model generation to library screening and bioinformatics analysis.
Contact EDITGENE today to design your custom CRISPR model for N-acetylmuramoyl-L-alanine amidase activity research.
Frequently Asked Questions About N-acetylmuramoyl-L-alanine amidase activity
What is N-acetylmuramoyl-L-alanine amidase activity?
It is an enzymatic activity (GO:0008745) that hydrolyzes the bond between N-acetylmuramoyl residues and L-amino acid residues in bacterial cell-wall glycopeptides, breaking down peptidoglycan.
What genes are involved in N-acetylmuramoyl-L-alanine amidase activity?
Genes include bacterial amidases such as ampD, amiA, amiB, amiC in E. coli, and mammalian PGLYRP2 (PGRP-L) and PGLYRP1 (PGRP-S).
What is the function of N-acetylmuramoyl-L-alanine amidase in bacteria?
It contributes to cell wall turnover, cell separation, autolysis, and peptidoglycan recycling, and can affect heterologous protein production.
How is N-acetylmuramoyl-L-alanine amidase activity measured?
It is measured using enzymatic assays with peptidoglycan or synthetic substrates, zymograms, or by detecting hydrolysis products via mass spectrometry.
What diseases are associated with N-acetylmuramoyl-L-alanine amidase?
Dysregulation is linked to inflammatory diseases and increased susceptibility to bacterial infections, while the enzyme itself is a potential antibacterial target.
Is N-acetylmuramoyl-L-alanine amidase found in humans?
Yes, human PGRP-L and PGRP-S possess this activity, and an amidase has been purified from human serum.
What is the role of zinc in N-acetylmuramoyl-L-alanine amidase?
Zinc is a cofactor for many amidases, including human PGRP-L, where it is essential for catalytic activity.
Can N-acetylmuramoyl-L-alanine amidase be used in biotechnology?
Yes, modulating its activity can enhance heterologous protein production by controlling cell lysis, and it has antimicrobial applications.
What are the synonyms for N-acetylmuramoyl-L-alanine amidase activity?
Synonyms include acetylmuramoyl-alanine amidase, N-acetylmuramyl-L-alanine amidase, and N-acetylmuramoyl-L-alanine amidase type I and II.
How can CRISPR be used to study N-acetylmuramoyl-L-alanine amidase activity?
CRISPR can create knockouts, point mutations, knock-ins, and overexpression models to dissect gene function and regulation in bacteria and mammalian cells.
Conclusion
N-acetylmuramoyl-L-alanine amidase activity (GO:0008745) is a fundamental enzymatic function that bridges bacterial cell wall biology and host immunity. Its roles in peptidoglycan turnover, bacterial cell division, and innate immune defense make it a compelling target for antibacterial drug discovery, biotechnological strain engineering, and immunological research. The availability of diverse experimental models, from bacterial knockouts to mammalian PGRP knockouts, enables precise interrogation of its mechanisms and physiological consequences. As research advances, targeting this activity may yield new strategies to combat infections and improve industrial processes.
References
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- 2. Lopez-Arvizu A et al.. 2021. Characterization of antibacterial activity of a N-acetylmuramoyl-L-alanine amidase produced by Latilactobacillus sakei isolated from salami.. World J Microbiol Biotechnol 37(4):65 PMID: 33740141
- 3. Parquet C et al.. 1983. N-acetylmuramoyl-L-alanine amidase of Escherichia coli K12. Possible physiological functions.. Eur J Biochem 133(2):371-7 PMID: 6133749
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- 5. Vanderwinkel E et al.. 1981. Activity of N-acetylmuramoyl-L-alanine amidase in phospholipidic environments.. Biochim Biophys Acta 663(1):46-57 PMID: 6111352
- 6. Wang ZM et al.. 2003. Human peptidoglycan recognition protein-L is an N-acetylmuramoyl-L-alanine amidase.. J Biol Chem 278(49):49044-52 PMID: 14506276
- 7. Gelius E et al.. 2003. A mammalian peptidoglycan recognition protein with N-acetylmuramoyl-L-alanine amidase activity.. Biochem Biophys Res Commun 306(4):988-94 PMID: 12821140
- 8. Vanderwinkel E et al.. 1990. Purification and characterization of N-acetylmuramoyl-L-alanine amidase from human serum.. Biochim Biophys Acta 1039(3):331-8 PMID: 1974148
