Maltodextrin phosphorylase

Last updated

Maltodextrin phosphorylase is a phosphorylase enzyme (EC 2.4.1.1), more specifically one type of glycosyltransferase (EC 2.4). Maltodextrin phosphorylase plays a critical role in maltodextrin metabolism in E. coli. This bacterial enzyme, often referred to as MalP, catalyzes the phosphorolysis of an α-1,4-glycosidic bond in maltodextrins, removing the non-reducing glucosyl residues of linear oligosaccharides as glucose-1-phosphate (Glc1P). Phosphorylases are well-regarded for their allosteric effects on metabolism, however MalP exhibits no allosteric properties. It has a higher affinity for linear oligosaccharides than the related glycogen phosphorylase. [1]

Contents

Mechanism

Maltodextrin phosphorylase facilitates maltodextrin metabolism through phosphorolysis of nonreducing glucosyl residues in order to produce Glc1P. MalP has a higher affinity for short, linear α-1,4 linked glucose oligosaccharides, and consequently appears to act on maltodextrin degradation products. [2] Without MalP, larger these products (typically composed of four or more glucosyl residues) are not degraded as easily for subsequent dextrin conversion into simple sugars [3]

[(1→4)-α-D-glucosyl](n) + Pi ⇌ [(1→4)-α-D-glucosyl](n-1) + α-D-glucose-1-phosphate. [4]

Previous study of the catalytic activity and kinetic properties of the MalP enzyme has revealed that it has different binding sites for the terminal glucose residue of the oligosaccharide and glucose-1-phosphate depending on whether its involvement is in the forward (phosphorylase) or reverse (synthesis) reaction. [2] Though the maltodextrin phosphorylase enzyme is capable of catalysis in both directions in vitro, its physiologically favored direction is as a phosphorylase.

Structure

The maltodextrin phosphorylase protomer is a large protein, composed of 796 amino acids with a mass of roughly 90 kDa in E. coli. While the enzyme can exist as an inactive monomer or tetramer, it is biologically active as a dimer of two identical subunits. Each MalP protomer contains one pyridoxal 5ʹ-phosphate cofactor in the active site, essential to catalytic activity. [5]

Application & Significance

No clinical significance of maltodextrin phosphorylase has been presently identified for use in humans; however, the enzyme may have biotechnological significance as it may allow for obtaining complex substrates for clinical research at less expense. Glc1P, a critical element to MalP’s phosphorolytic bioconversion process and a rather expensive chemical, can be enzymatically derived from dextrins or other starchy materials. [6]

Regulation

Maltodextrin phosphorylase readily catalyzes the reverse reaction of Glc1P plus oligosaccharide to yield an oligosaccharide lengthened by one glucose residue and liberation of inorganic phosphate. The sequence of E. coli MalP is nearly 100% identical to the mammalian glycogen phosphorylase (GP) at the catalytic site. In comparison to the mammalian GP, MalP is a simpler enzyme. It is regulated neither by allosteric effectors nor phosphorylation and it is expressed in E. coli as a constitutively active enzyme. [1]

Crystal structures of oligosaccharide bound across the catalytic site in both the binary and the ternary MalP enzyme/substrate complexes reveal the importance of the conformational change in the oligosaccharide substrate in the formation of ternary complexes and provides support for the role of the 50-phosphate group of pyridoxal phosphate (PLP) in catalysis. [1]

Related Research Articles

<span class="mw-page-title-main">Glycogenolysis</span> Breakdown of glycogen

Glycogenolysis is the breakdown of glycogen (n) to glucose-1-phosphate and glycogen (n-1). Glycogen branches are catabolized by the sequential removal of glucose monomers via phosphorolysis, by the enzyme glycogen phosphorylase.

<span class="mw-page-title-main">Aspartate carbamoyltransferase</span> Protein family

Aspartate carbamoyltransferase catalyzes the first step in the pyrimidine biosynthetic pathway.

<span class="mw-page-title-main">Pyridoxal phosphate</span> Active form of vitamin B6

Pyridoxal phosphate (PLP, pyridoxal 5'-phosphate, P5P), the active form of vitamin B6, is a coenzyme in a variety of enzymatic reactions. The International Union of Biochemistry and Molecular Biology has catalogued more than 140 PLP-dependent activities, corresponding to ~4% of all classified activities. The versatility of PLP arises from its ability to covalently bind the substrate, and then to act as an electrophilic catalyst, thereby stabilizing different types of carbanionic reaction intermediates.

<span class="mw-page-title-main">Phosphorylase</span> Class of enzymes

In biochemistry, phosphorylases are enzymes that catalyze the addition of a phosphate group from an inorganic phosphate (phosphate+hydrogen) to an acceptor.

<span class="mw-page-title-main">Aspartate transaminase</span> Enzyme involved in amino acid metabolism

Aspartate transaminase (AST) or aspartate aminotransferase, also known as AspAT/ASAT/AAT or (serum) glutamic oxaloacetic transaminase, is a pyridoxal phosphate (PLP)-dependent transaminase enzyme that was first described by Arthur Karmen and colleagues in 1954. AST catalyzes the reversible transfer of an α-amino group between aspartate and glutamate and, as such, is an important enzyme in amino acid metabolism. AST is found in the liver, heart, skeletal muscle, kidneys, brain, red blood cells and gall bladder. Serum AST level, serum ALT level, and their ratio are commonly measured clinically as biomarkers for liver health. The tests are part of blood panels.

Glycogenesis is the process of glycogen synthesis or the process of converting glucose into glycogen in which glucose molecules are added to chains of glycogen for storage. This process is activated during rest periods following the Cori cycle, in the liver, and also activated by insulin in response to high glucose levels.

<span class="mw-page-title-main">Glycogen phosphorylase</span> Class of enzymes

Glycogen phosphorylase is one of the phosphorylase enzymes. Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Glycogen phosphorylase is also studied as a model protein regulated by both reversible phosphorylation and allosteric effects.

<span class="mw-page-title-main">Glycogen synthase</span> Enzyme class, includes all types of glycogen/starch synthases

Glycogen synthase is a key enzyme in glycogenesis, the conversion of glucose into glycogen. It is a glycosyltransferase that catalyses the reaction of UDP-glucose and n to yield UDP and n+1.

<span class="mw-page-title-main">Glycogen debranching enzyme</span> Mammalian protein found in Homo sapiens

The glycogen debranching enzyme, in humans, is the protein encoded by the gene AGL. This enzyme is essential for the breakdown of glycogen, which serves as a store of glucose in the body. It has separate glucosyltransferase and glucosidase activities.

<span class="mw-page-title-main">Glycogen branching enzyme</span> Mammalian protein involved in glycogen production

1,4-alpha-glucan-branching enzyme, also known as brancher enzyme or glycogen-branching enzyme is an enzyme that in humans is encoded by the GBE1 gene.

<span class="mw-page-title-main">Phosphorylase kinase</span>

Phosphorylase kinase (PhK) is a serine/threonine-specific protein kinase which activates glycogen phosphorylase to release glucose-1-phosphate from glycogen. PhK phosphorylates glycogen phosphorylase at two serine residues, triggering a conformational shift which favors the more active glycogen phosphorylase "a" form over the less active glycogen phosphorylase b.

<span class="mw-page-title-main">Myophosphorylase</span> Muscle enzyme involved in glycogen breakdown

Myophosphorylase or glycogen phosphorylase, muscle associated (PYGM) is the muscle isoform of the enzyme glycogen phosphorylase and is encoded by the PYGM gene. This enzyme helps break down glycogen into glucose-1-phosphate, so it can be used within the muscle cell. Mutations in this gene are associated with McArdle disease, a glycogen storage disease of muscle.

<span class="mw-page-title-main">Sucrose phosphorylase</span> Class of enzymes

Sucrose phosphorylase is an important enzyme in the metabolism of sucrose and regulation of other metabolic intermediates. Sucrose phosphorylase is in the class of hexosyltransferases. More specifically it has been placed in the retaining glycoside hydrolases family although it catalyzes a transglycosidation rather than hydrolysis. Sucrose phosphorylase catalyzes the conversion of sucrose to D-fructose and α-D-glucose-1-phosphate. It has been shown in multiple experiments that the enzyme catalyzes this conversion by a double displacement mechanism.

<span class="mw-page-title-main">Cystathionine beta-lyase</span> Enzyme

Cystathionine beta-lyase, also commonly referred to as CBL or β-cystathionase, is an enzyme that primarily catalyzes the following α,β-elimination reaction

<span class="mw-page-title-main">Arginine decarboxylase</span>

The enzyme Acid-Induced Arginine Decarboxylase (AdiA), also commonly referred to as arginine decarboxylase, catalyzes the conversion of L-arginine into agmatine and carbon dioxide. The process consumes a proton in the decarboxylation and employs a pyridoxal-5'-phosphate (PLP) cofactor, similar to other enzymes involved in amino acid metabolism, such as ornithine decarboxylase and glutamine decarboxylase. It is found in bacteria and virus, though most research has so far focused on forms of the enzyme in bacteria. During the AdiA catalyzed decarboxylation of arginine, the necessary proton is consumed from the cell cytoplasm which helps to prevent the over-accumulation of protons inside the cell and serves to increase the intracellular pH. Arginine decarboxylase is part of an enzymatic system in Escherichia coli, Salmonella Typhimurium, and methane-producing bacteria Methanococcus jannaschii that makes these organisms acid resistant and allows them to survive under highly acidic medium.

<span class="mw-page-title-main">N-acetylglucosamine-6-phosphate deacetylase</span>

In enzymology, N-acetylglucosamine-6-phosphate deacetylase (EC 3.5.1.25), also known as GlcNAc-6-phosphate deacetylase or NagA, is an enzyme that catalyzes the deacetylation of N-acetylglucosamine-6-phosphate (GlcNAc-6-P) to glucosamine-6-phosphate (GlcN-6-P):

Xanthosine phosphorylase, also known as inosine-guanosine phosphorylase, is a catalytic enzyme encoded by the XapA gene in E. coli. The presence of xanthosine is known to induce the synthesis of xanthosine phosphorylase by the XapA gene. The enzyme's main functions are nucleoside phosphorolysis and the synthesis of nucleotides, making it a member of the purine nucleoside phosphorylase group. This protein can degrade all purine nucleosides except adenosine, deoxyadenosine, hypoxanthine arabinoside. These degradation reactions are reversible in vitro, however, phosphorolysis dominates in vivo. Xanthosine phosphorylase is localized in the cytoplasm because these degradation functions take place there. Xanthosine phosphorylase preferentially uses the neutral form of xanthosine over its monoanionic form because it prefers to be in a neutral environment.

N,N'-diacetylchitobiose phosphorylase is an enzyme with the systematic name N,N'-diacetylchitobiose:phosphate N-acetyl-D-glucosaminyltransferase. This enzyme was found in the genus Vibrio initially but has now been found to be taken up by Escherichia coli as well as many other bacteria. One study shows that Escherichia coli can replicate on a medium that is just composed of GlcNAc a product of phosphorylation of N,N'-diacetylchitobiose as the sole source of carbon. Because E. coli can go on this medium, the enzyme is present. The enzyme has also been found in multiple eukaryotic cells as well, especially in eukaryotes that make chitin and break chitin down. It is believed that N,N'-diacetylchitobiose phosphorylase is an integral part of the phosphoenolpyruvate:glucose phosphotransferase system (PTS). It is assumed that it is involved with Enzyme Complex II of the PTS and is involved with the synthesis of chitin. The enzyme is specific for N,N'-diacetylchitobiose.

In bacterial genetics, the mal regulon is a regulon - or group of genes under common regulation - associated with the catabolism of maltose and maltodextrins. The system is especially well characterized in the model organism Escherichia coli, where it is classically described as a group of ten genes in multiple operons whose expression is regulated by a single regulatory protein, malT. MalT binds to maltose or maltodextrin and undergoes a conformational change that allows it to bind DNA at sequences near the promoters of genes required for uptake and catabolism of these sugars. The maltose regulation system in E. coli is a classic example of positive regulation. malT is regulated by catabolite repression via the catabolite activator protein. Genes under the control of malT include ATP-binding cassette transporter components, maltoporin, maltose binding protein, and several enzymes. Other Gram-negative bacteria such as Klebsiella pneumoniae have additional genes under the control of malT.

Glycogen phosphorylase, liver form (PYGL), also known as human liver glycogen phosphorylase (HLGP), is an enzyme that in humans is encoded by the PYGL gene on chromosome 14. This gene encodes a homodimeric protein that catalyses the cleavage of alpha-1,4-glucosidic bonds to release glucose-1-phosphate from liver glycogen stores. This protein switches from inactive phosphorylase B to active phosphorylase A by phosphorylation of serine residue 14. Activity of this enzyme is further regulated by multiple allosteric effectors and hormonal controls. Humans have three glycogen phosphorylase genes that encode distinct isozymes that are primarily expressed in liver, brain and muscle, respectively. The liver isozyme serves the glycemic demands of the body in general while the brain and muscle isozymes supply just those tissues. In glycogen storage disease type VI, also known as Hers disease, mutations in liver glycogen phosphorylase inhibit the conversion of glycogen to glucose and results in moderate hypoglycemia, mild ketosis, growth retardation and hepatomegaly. Alternative splicing results in multiple transcript variants encoding different isoforms [provided by RefSeq, Feb 2011].

References

  1. 1 2 3 Geremia, S; Campagnolo, M; Schinzel, R; Johnson, L N (September 13, 2002). "Enzymatic catalysis in crystals of Escherichia coli maltodextrin phosphorylase". Journal of Molecular Biology. 322 (2): 413–423. doi:10.1016/s0022-2836(02)00771-4. PMID   12217700.
  2. 1 2 "Maltodextrin phosphorylase". biocyc.org. Retrieved 10 December 2023.
  3. ↑ Dippel, Renate; Boos, Winfried (December 15, 2005). "The Maltodextrin System of Escherichia coli: Metabolism and Transport". Journal of Bacteriology. 187 (24): 8322–8331. doi: 10.1128/JB.187.24.8322-8331.2005 . PMC   1316994 . PMID   16321936.
  4. ↑ "KEGG REACTION: R01821". www.genome.jp. Retrieved 2023-12-14.
  5. ↑ Greißler, Richard; D'Auria, Sabato; Schinzel, Reinhard; Tanfani, Fabio; Nidetzky, Bernd (March 1, 2000). "Mechanism of thermal denaturation of maltodextrin phosphorylase from Escherichia coli". Biochemical Journal. 346 (Pt 2): 255–263. doi:10.1042/bj3460255. PMC   1220849 . PMID   10677342.
  6. ↑ Weinhäusel, Andreas; Nidetzky, Bernd; Kysela, Christian; Kulbe, Klaus D. (February 1995). "Application of Escherichia coli maltodextrin-phosphorylase for the continuous production of glucose-1-phosphate". Enzyme and Microbial Technology. 17 (2): 140–146. doi:10.1016/0141-0229(94)00055-V.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.