DNA-3-methyladenine glycosylase

(Redirected from MPG (gene)) Protein-coding gene in the species Homo sapiens

MPG

Available structures

Ortholog search: PDBe RCSB

List of PDB id codes
1BNK, 1EWN, 1F4R, 1F6O, 3QI5, 3UBY

Identifiers

Aliases

MPG, AAG, ADPG, APNG, CRA36.1, MDG, Mid1, PIG11, PIG16, anpg, N-methylpurine DNA glycosylase

External IDs

OMIM: 156565; MGI: 97073; HomoloGene: 1824; GeneCards: MPG; OMA:MPG - orthologs

Gene location (Human)

Chr.	Chromosome 16 (human)

Band	16p13.3	Start	77,007 bp
Band	16p13.3	End	85,851 bp

Gene location (Mouse)

Chr.	Chromosome 11 (mouse)

Band	11 A4\|11 18.83 cM	Start	32,176,505 bp
Band	11 A4\|11 18.83 cM	End	32,182,700 bp

RNA expression pattern

Bgee

Human

Mouse (ortholog)

Top expressed in

ascending aorta

Descending thoracic aorta

right coronary artery

stromal cell of endometrium

left coronary artery

tibial arteries

gastric mucosa

left adrenal cortex

right lung

right adrenal gland

Top expressed in

parotid gland

proximal tubule

seminal vesicula

efferent ductule

renal corpuscle

fossa

right kidney

lumbar subsegment of spinal cord

molar

seminiferous tubule

More reference expression data

BioGPS


More reference expression data

Gene ontology
Molecular function	DNA-7-methylguanine glycosylase activity DNA-7-methyladenine glycosylase activity damaged DNA binding DNA binding alkylbase DNA N-glycosylase activity protein binding DNA-3-methylguanine glycosylase activity catalytic activity hydrolase activity DNA-3-methyladenine glycosylase activity DNA N-glycosylase activity
Cellular component	cytoplasm mitochondrial nucleoid mitochondrion nucleus nucleoplasm
Biological process	depurination DNA dealkylation involved in DNA repair base-excision repair cellular response to DNA damage stimulus DNA repair
Sources:Amigo / QuickGO

Orthologs

Species

Human

Mouse

Entrez


4350


268395

Ensembl


ENSG00000103152


ENSMUSG00000020287

UniProt


P29372


Q04841

RefSeq (mRNA)


NM_002434 NM_001015052 NM_001015054


NM_010822

RefSeq (protein)


NP_001015052 NP_001015054 NP_002425


NP_034952

Location (UCSC)

Chr 16: 0.08 – 0.09 Mb

Chr 11: 32.18 – 32.18 Mb

PubMed search

Wikidata

View/Edit Human

View/Edit Mouse

DNA-3-methyladenine glycosylase also known as 3-alkyladenine DNA glycosylase (AAG) or N-methylpurine DNA glycosylase (MPG) is an enzyme that in humans is encoded by the MPG gene.

Alkyladenine DNA glycosylase is a specific type of DNA glycosylase. This subfamily of monofunctional glycosylases is involved in the recognition of a variety of base lesions, including alkylated and deaminated purines, and initiating their repair via the base excision repair pathway. To date, the human AAG (hAAG) is the only glycosylase identified that excises alkylation-damaged purine bases in human cells.

Function

DNA bases are subject to a large number of anomalies: spontaneous alkylation or oxidative deamination. It is estimated that 10 mutations appear in a typical human cell per day. Albeit it seems to be an insignificant amount considering the extension of the DNA (10 nucleotides), these mutations lead to changes in the structure and coding potential of the DNA, affecting processes of replication and transcription.

3-Methyladenine DNA glycosylases are able to initiate the base excision repair (BER) of a wide range of substrate bases that, due to their chemical reactivity, suffer inevitable modifications resulting in different biological outcomes. DNA repair mechanisms take on a vital role in maintaining the genomic integrity of cells from different organisms, in particular 3-Methyladenine DNA glycosylases are found in bacteria, yeast, plants, rodents, and humans. Therefore, there are different subfamilies of this enzyme, such as the Human Alkyladenine DNA Glycosylase (hAAG), that act on other damaged DNA bases apart from 3-MeA.

Table that shows the presence (+) or absence (-) of biochemical activity between the different subfamilies of the DNA-3-methyladenine glycosylase and the different types of damaged DNA bases
	tag	AlkA	MAG	mag1	ADPG	Aag	AGG	aMAG
3-MeA	+	+	+	+	+	+	+	+
3-MeG	+	+	+			+	+	+
7-MeG	-	+	+	+	+	+	+	+
O2-MeG	-	+
O2-MeC	-	+
7-CEG		+	+
7-HEG		+	+
7-EthoxyG		+
eA	-	+	+		+	+	+	+
eG							+
8-oxoG						+	+
Hx	-	+	+		+	+	+	+
A		+			+
G	-	+	+		+	+
T		+
C		+

Alkylation repairing activity

In cells, AAG is the enzyme responsible for recognition and initiation of the repair, via catalysing the hydrolysis of the N-glycosidic bond to release the alkylation-damaged purine bases. Specifically, hAAG is able to efficiently identify and excise 3-methyladenine, 7-methyladenine, 7-methylguanine, 1N-ethenoadenine and hypoxanthine.

Deaminated base activity

MPG can act on all three purine deamination bases: hypoxanthine, xanthine, and oxanine.

Oxanine (Oxa), is a deaminated base lesion in which the N1-nitrogen is replaced by oxygen. Contrary to the alkylation repairing activity, which is only able to act against purine bases, the hAAG is able to excise Oxa from all of four Oxa-containing double stranded base pairs, Cyt/Oxa, Thy/Oxa, Ade/Oxa, and Gua/Oxa, showing no particular preference by any of the bases. In addition hAAG is capable of removing Oxa from single-stranded Oxa- containing DNA. This occurs because the ODG activity of the hAAG does not require a complementary strand.

Structure

Alkyladenine DNA glycosylase is a monomeric protein compounded by 298 amino acids, with a formula weight of 33kDa. Its canonical primary structure consists of the following sequence. However, also other functional isoforms have been found.

PDB rendering based on 1F6O — Human Alkyladenine DNA Glycosylase's structure generated with Pymol

Isoform 2

The sequence of this isoform differs from the canonical sequence as follows:

Aminoacids 1-12: MVTPALQMKKPK → MPARSGA

Aminoacids 195-196: QL →HV

Isoform 3

The sequence of this isoform differs from the canonical sequence in a similar way as the isoform 2:

Aminoacids 1-12: MVTPALQMKKPK → MPARSGA

Isoform 4

The sequence of this isoform misses the aminoacids 1–17.

It folds into a single domain of mixed α/β structure, with seven α helices and eight β strands. The core of the protein consists of a curved, antiparallel β sheet with a protruding β hairpin (β3β4) that inserts into the minor groove of the bound DNA. A series of α helices and connecting loops form the remainder of the DNA binding interface. It lacks the helix-hairpin-helix motif associated with other base excision-repair proteins and, in fact, it does not resemble any other model in the Protein Data Bank.

Mechanism

Substrate recognition

Alkyladenine DNA glycosylase is part of the family of enzymes that follow the BER, acting on specific substrates according to BER steps.

The process of recognition of damaged bases involves initial non-specific binding followed by diffusion along the DNA. Formed the AAG-DNA complex, a redundant process of search occurs because of the long lifetime of this complex, while hAAG search many adjacent sites in a DNA molecule in a single binding. This provides ample opportunity to recognize and excise lesions that minimally perturb the structure of the DNA.

Due to its broad specificity, the hAAG performs the substrate selection through a combination of selectivity filters.

The first selectivity filter occurs at the nucleotide flipping step of unusable base pairs that present lesions.
The second selectivity filter is constituted by the catalytic mechanism which ensures that only purine bases are excised, even though smaller pyrimidines can fit in the hAAG's active site. The active site pocket it's designed to accommodate a structurally diverse set of modified purines so it would be difficult to sterically exclude the smaller pyrimidine bases from binding. However, thanks to the different shape and chemical properties of a bound pyrimidine and a purine substrate, the acid-catalyzed reacts only with the pyrimidine preventing it from binding with the hAAG.
The third selectivity filter consist of unfavorable steric clashes that allow a preferential recognition of purine lesions lacking exocyclic amino groups of guanine and adenine.
Schematic diagram of hAAG-DNA contacts

Nucleotide flipping and fixation

Its structure contains an antiparallel β sheet with protruding β hairpin (β3β4) that inserts into the minor groove of the bound DNA. This group is unique for the human cells and displaces the selected nucleotide targeted for base excision by flipping it. The nucleotide is secured into the enzyme binding pocket where the active site is found, and is fixed by the amino acids Arg182, Glu125 and Ser262. Also other bonds are formed to bordering nucleotides to stabilize the structure.

The groove in the double helix of DNA left by the flipped-out abasic nucleotide is filled with the lateral chain of the amino acid Tyr162, making no specific contacts with the surrounding bases.

Nucleotide release

Activated by nearby aminoacids, a water molecule attacks the N-Glycosydic bound releasing the alkylated base via a backside displacement mechanism.

Location

Human alkyladenine DNA glycosylase localizes to the mitochondria, nucleus and cytoplasm of human cells. Some functionally equivalent enzymes have been found in other species have significantly different structures, such as DNA-3-methyladenine glycosylase in E. coli.

Clinical significance

According to the mechanism used by Human Alkyladenine DNA Glycosylase, a defect in the DNA repair pathways leads to cancer predisposition. HAAG follows the BER steps so that means that an incorrect role of BER genes could contribute to the development of cancer. Concretely, a bad activity of hAAG may be associated with cancer risk in BRCA1 and BRCA2 mutation carriers.

Aging

As noted above, DNA-3-methyladenine glycosylase (also called 3-alklyadeneine DNA glycosylase or AAG) is able to identify and excise a variety of alkylation damaged purine bases. Such damages to purine bases occur spontaneously in DNA. Double-mutant mice deficient both for AAG and another enzyme that specifically repairs O6MeG damages (O-6-methylguanine-DNA methyltransferase) had a shorter lifespan and aged more rapidly than wild type mice. These findings indicate that damaged purine bases contribute to the aging process, consistent with the DNA damage theory of aging.

References

^ GRCh38: Ensembl release 89: ENSG00000103152 – Ensembl, May 2017
^ GRCm38: Ensembl release 89: ENSMUSG00000020287 – Ensembl, May 2017
"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
Chakravarti D, Ibeanu GC, Tano K, Mitra S (Aug 1991). "Cloning and expression in Escherichia coli of a human cDNA encoding the DNA repair protein N-methylpurine-DNA glycosylase". The Journal of Biological Chemistry. 266 (24): 15710–5. doi:10.1016/S0021-9258(18)98467-X. PMID 1874728.
"Entrez Gene: MPG N-methylpurine-DNA glycosylase".
Hedglin M, O'Brien PJ (2008). "Human alkyladenine DNA glycosylase employs a processive search for DNA damage". Biochemistry. 47 (44): 11434–45. doi:10.1021/bi801046y. PMC 2702167. PMID 18839966.
Abner CW, Lau AY, Ellenberger T, Bloom LB (Apr 2001). "Base excision and DNA binding activities of human alkyladenine DNA glycosylase are sensitive to the base paired with a lesion". The Journal of Biological Chemistry. 276 (16): 13379–87. doi:10.1074/jbc.M010641200. PMID 11278716.
Wyatt MD, Allan JM, Lau AY, Ellenberger TE, Samson LD (August 1999). "3-methyladenine DNA glycosylases: structure, function, and biological importance". BioEssays. 21 (8): 668–676. doi:10.1002/(SICI)1521-1878(199908)21:8<668::AID-BIES6>3.0.CO;2-D. PMID 10440863. S2CID 29109365.
^ O'Brien PJ, Ellenberger T (Oct 2003). "Human alkyladenine DNA glycosylase uses acid-base catalysis for selective excision of damaged purines". Biochemistry. 42 (42): 12418–29. doi:10.1021/bi035177v. PMID 14567703.
Admiraal SJ, O'Brien PJ (Oct 2010). "N-glycosyl bond formation catalyzed by human alkyladenine DNA glycosylase". Biochemistry. 49 (42): 9024–6. doi:10.1021/bi101380d. PMC 2975558. PMID 20873830.
Hollis T, Lau A, Ellenberger T (Aug 2000). "Structural studies of human alkyladenine glycosylase and E. coli 3-methyladenine glycosylase". Mutation Research. 460 (3–4): 201–10. doi:10.1016/S0921-8777(00)00027-6. PMID 10946229.
Hitchcock, Thomas M.; Dong, Liang; Connor, Ellen E.; Meira, Lisiane B.; Samson, Leona D.; Wyatt, Michael D.; Cao, Weiguo (2004). "Oxanine DNA Glycosylase Activity from Mammalian Alkyladenine Glycosylase". Journal of Biological Chemistry. 279 (37): 38177–38183. doi:10.1074/jbc.m405882200. ISSN 0021-9258. PMID 15247209.
Hitchcock TM, Dong L, Connor EE, Meira LB, Samson LD, Wyatt MD, Cao W (Sep 2004). "Oxanine DNA glycosylase activity from Mammalian alkyladenine glycosylase". The Journal of Biological Chemistry. 279 (37): 38177–83. doi:10.1074/jbc.M405882200. PMID 15247209.
^ Lau AY, Schärer OD, Samson L, Verdine GL, Ellenberger T (Oct 1998). "Crystal structure of a human alkylbase-DNA repair enzyme complexed to DNA: mechanisms for nucleotide flipping and base excision". Cell. 95 (2): 249–58. doi:10.1016/S0092-8674(00)81755-9. PMID 9790531. S2CID 14125483.
Zhang, Yaru (2014). Specificity and Searching Mechanism of Alkyladenine DNA Glycosylase (Thesis). hdl:2027.42/110472.
Hedglin M, O'Brien PJ (2008). "Human Alkyladenine DNA Glycosylase employs a processive search for dNA damage". Biochemistry. 47 (44): 11434–11445. doi:10.1021/bi801046y. PMC 2702167. PMID 18839966.
van Loon B, Samson LD (Mar 2013). "Alkyladenine DNA glycosylase (AAG) localizes to mitochondria and interacts with mitochondrial single-stranded binding protein (mtSSB)" (PDF). DNA Repair. 12 (3): 177–87. doi:10.1016/j.dnarep.2012.11.009. hdl:1721.1/99514. PMC 3998512. PMID 23290262.
Osorio A, Milne RL, Kuchenbaecker K, Vaclová T, Pita G, Alonso R, et al. (Apr 2014). "DNA glycosylases involved in base excision repair may be associated with cancer risk in BRCA1 and BRCA2 mutation carriers". PLOS Genetics. 10 (4): e1004256. doi:10.1371/journal.pgen.1004256. PMC 3974638. PMID 24698998.
Meira LB, Calvo JA, Shah D, Klapacz J, Moroski-Erkul CA, Bronson RT, Samson LD (September 2014). "Repair of endogenous DNA base lesions modulate lifespan in mice". DNA Repair. 21: 78–86. doi:10.1016/j.dnarep.2014.05.012. PMC 4125484. PMID 24994062.

External links

DNA-3-methyladenine+glycosylase+II at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

v t e PDB gallery
1bnk: HUMAN 3-METHYLADENINE DNA GLYCOSYLASE COMPLEXED TO DNA 1ewn: CRYSTAL STRUCTURE OF THE HUMAN AAG DNA REPAIR GLYCOSYLASE COMPLEXED WITH 1,N6-ETHENOADENINE-DNA 1f4r: CRYSTAL STRUCTURE OF THE HUMAN AAG DNA REPAIR GLYCOSYLASE COMPLEXED WITH 1,N6-ETHENOADENINE-DNA 1f6o: CRYSTAL STRUCTURE OF THE HUMAN AAG DNA REPAIR GLYCOSYLASE COMPLEXED WITH DNA

Hydrolase: sugar hydrolases (EC 3.2)

3.2.1: Glycoside hydrolases

Disaccharidase	Sucrase/Sucrase-isomaltase/Invertase Maltase Trehalase Lactase
Glucosidases	Cellulase Alpha-glucosidase Acid Neutral AB Neutral C Beta-glucosidase cytosolic Debranching enzyme
Other	Amylase Alpha-amylase Chitinase Lysozyme Neuraminidase NEU1 NEU2 NEU3 NEU4 Bacterial neuraminidase Viral neuraminidase Galactosidases Alpha Beta alpha-Mannosidase Glucuronidase Klotho Hyaluronidase Pullulanase Glucosylceramidase lysosomal non-lysosomal Galactosylceramidase Alpha-N-acetylgalactosaminidase NAGA Alpha-N-acetylglucosaminidase Fucosidase Hexosaminidase HEXA HEXB Iduronidase Maltase-glucoamylase Heparanase HPSE2

3.2.2: Hydrolysing
N-Glycosyl compounds

DNA glycosylases: Oxoguanine glycosylase

v t e Enzymes
Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis
Regulation	Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator
Classification	EC number Enzyme superfamily Enzyme family List of enzymes
Kinetics	Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics
Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)