ID   MTNN_KLEPN              Reviewed;          35 AA.
AC   Q9R4A1;
DT   20-JAN-2009, integrated into UniProtKB/Swiss-Prot.
DT   01-MAY-2000, sequence version 1.
DT   03-AUG-2022, entry version 64.
DE   RecName: Full=5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase;
DE            Short=MTA/SAH nucleosidase;
DE            Short=MTAN;
DE            EC=3.2.2.9 {ECO:0000269|PubMed:8694776};
DE   AltName: Full=5'-deoxyadenosine nucleosidase {ECO:0000250|UniProtKB:P0AF12};
DE            Short=DOA nucleosidase {ECO:0000250|UniProtKB:P0AF12};
DE            Short=dAdo nucleosidase {ECO:0000250|UniProtKB:P0AF12};
DE   AltName: Full=5'-methylthioadenosine nucleosidase;
DE            Short=MTA nucleosidase;
DE   AltName: Full=S-adenosylhomocysteine nucleosidase;
DE            Short=AdoHcy nucleosidase;
DE            Short=SAH nucleosidase;
DE            Short=SRH nucleosidase;
DE   Flags: Fragment;
GN   Name=mtnN;
OS   Klebsiella pneumoniae.
OC   Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacterales;
OC   Enterobacteriaceae; Klebsiella/Raoultella group; Klebsiella.
OX   NCBI_TaxID=573;
RN   [1]
RP   PROTEIN SEQUENCE, FUNCTION AS MTA NUCLEOSIDASE, CATALYTIC ACTIVITY, AND
RP   KINETIC PARAMETERS.
RX   PubMed=8694776; DOI=10.1042/bj3170285;
RA   Cornell K.A., Winter R.W., Tower P.A., Riscoe M.K.;
RT   "Affinity purification of 5-methylthioribose kinase and 5-
RT   methylthioadenosine/S-adenosylhomocysteine nucleosidase from Klebsiella
RT   pneumoniae.";
RL   Biochem. J. 317:285-290(1996).
CC   -!- FUNCTION: Catalyzes the irreversible cleavage of the glycosidic bond in
CC       both 5'-methylthioadenosine (MTA) and S-adenosylhomocysteine
CC       (SAH/AdoHcy) to adenine and the corresponding thioribose, 5'-
CC       methylthioribose and S-ribosylhomocysteine, respectively
CC       (PubMed:8694776). Also cleaves 5'-deoxyadenosine, a toxic by-product of
CC       radical S-adenosylmethionine (SAM) enzymes, into 5-deoxyribose and
CC       adenine. Thus, is required for in vivo function of the radical SAM
CC       enzymes biotin synthase and lipoic acid synthase, that are inhibited by
CC       5'-deoxyadenosine accumulation (By similarity).
CC       {ECO:0000250|UniProtKB:P0AF12, ECO:0000269|PubMed:8694776}.
CC   -!- CATALYTIC ACTIVITY:
CC       Reaction=H2O + S-adenosyl-L-homocysteine = adenine + S-(5-deoxy-D-
CC         ribos-5-yl)-L-homocysteine; Xref=Rhea:RHEA:17805, ChEBI:CHEBI:15377,
CC         ChEBI:CHEBI:16708, ChEBI:CHEBI:57856, ChEBI:CHEBI:58195; EC=3.2.2.9;
CC         Evidence={ECO:0000269|PubMed:8694776};
CC   -!- CATALYTIC ACTIVITY:
CC       Reaction=H2O + S-methyl-5'-thioadenosine = 5-(methylsulfanyl)-D-ribose
CC         + adenine; Xref=Rhea:RHEA:13617, ChEBI:CHEBI:15377,
CC         ChEBI:CHEBI:16708, ChEBI:CHEBI:17509, ChEBI:CHEBI:78440; EC=3.2.2.9;
CC         Evidence={ECO:0000269|PubMed:8694776};
CC   -!- CATALYTIC ACTIVITY:
CC       Reaction=5'-deoxyadenosine + H2O = 5-deoxy-D-ribose + adenine;
CC         Xref=Rhea:RHEA:29859, ChEBI:CHEBI:15377, ChEBI:CHEBI:16708,
CC         ChEBI:CHEBI:17319, ChEBI:CHEBI:149540; EC=3.2.2.9;
CC         Evidence={ECO:0000250|UniProtKB:P0AF12};
CC       PhysiologicalDirection=left-to-right; Xref=Rhea:RHEA:29860;
CC         Evidence={ECO:0000250|UniProtKB:P0AF12};
CC   -!- BIOPHYSICOCHEMICAL PROPERTIES:
CC       Kinetic parameters:
CC         KM=8.7 uM for 5'-methylthioadenosine (at pH 7 and 37 degrees Celsius)
CC         {ECO:0000269|PubMed:8694776};
CC   -!- PATHWAY: Amino-acid biosynthesis; L-methionine biosynthesis via salvage
CC       pathway; S-methyl-5-thio-alpha-D-ribose 1-phosphate from S-methyl-5'-
CC       thioadenosine (hydrolase route): step 1/2.
CC       {ECO:0000250|UniProtKB:P0AF12}.
CC   -!- SUBUNIT: Homodimer. {ECO:0000250|UniProtKB:P0AF12}.
CC   -!- SIMILARITY: Belongs to the PNP/UDP phosphorylase family. MtnN
CC       subfamily. {ECO:0000305}.
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DR   AlphaFoldDB; Q9R4A1; -.
DR   SMR; Q9R4A1; -.
DR   BioCyc; MetaCyc:MON-1288; -.
DR   UniPathway; UPA00904; UER00871.
DR   GO; GO:0008782; F:adenosylhomocysteine nucleosidase activity; IEA:UniProtKB-EC.
DR   GO; GO:0008930; F:methylthioadenosine nucleosidase activity; IEA:RHEA.
DR   GO; GO:0019509; P:L-methionine salvage from methylthioadenosine; IEA:UniProtKB-UniPathway.
PE   1: Evidence at protein level;
KW   Amino-acid biosynthesis; Direct protein sequencing; Hydrolase;
KW   Methionine biosynthesis.
FT   CHAIN           1..>35
FT                   /note="5'-methylthioadenosine/S-adenosylhomocysteine
FT                   nucleosidase"
FT                   /id="PRO_0000359310"
FT   ACT_SITE        12
FT                   /note="Proton acceptor"
FT                   /evidence="ECO:0000250"
FT   NON_TER         35
SQ   SEQUENCE   35 AA;  3924 MW;  FB878C0271A01C35 CRC64;
     MKIGIIGAME EEVTLLRDKI ENRQTITIGG SEIYT