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NT5C
5', 3'-nucleotidase, cytosolic, also known as 5'(3')-deoxyribonucleotidase, cytosolic type (cdN) or deoxy-5'-nucleotidase 1 (dNT-1), is an enzyme that in humans is encoded by the ''NT5C'' gene on chromosome 17.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=30833 )〕〔(【引用サイトリンク】 url = http://www.uniprot.org/uniprot/Q8TCD5 )〕
==Structure==
cdN is one of seven 5' nucleotidases identified in humans, all of which differ in tissue specificity, subcellular location, primary structure and substrate specificity. Of the seven, the mitochondrial counterpart of cdN, mdN, is the most closely related to cdN. Their genes, ''NT5M'' and ''NT5C'', share the same exon/intron organization, and their amino acid sequences are 52% identical.〔〔〔 Both cdN and mdN share nearly identical catalytic phosphate binding sites with most members of the haloacid dehalogenase (HAD) superfamily.〔
This enzyme forms a 45-kDa homodimer of two 22-kDa subunits composed of a core domain and cap domain.〔 The core domain is an α/β Rossmann-like fold containing six antiparallel β-strands surrounded by α-helixes, and it spans residues 1-17 and 77-201 of the amino acid sequence. The cap domain is a 4-helix bundle spanning residues 18-76. The cleft formed by the core and cap domains acts as the enzyme’s active site, where three conserved motifs in the core domain plus the cofactor Mg2+ serve as the substrate binding site. Meanwhile, the residues Phe18, Phe44, Leu45, and Tyr65 in the cap domain form an aromatic, hydrophobic pocket that coordinates with the base of the nucleotide substrate and, thus, influences the enzyme’s substrate specificity. Its two main chain amides form hydrogen bonds with the 4-carbonyl group of dUMP and dTMP and with the 6-carbonyl group of dGMP and dIMP, while repelling the 4-amino group of dCMP and dAMP. The residue Asp43 is responsible for donating a proton to O5’ of the nucleotide during catalysis.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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