학술논문
5′‐Nucleotidase
Document Type
Reference
Author
Norbert Sträter, author
Source
Encyclopedia of Inorganic and Bioinorganic Chemistry.
Subject
Language
English
Abstract
Escherichia coli 5′‐nucleotidase (5′‐NT) is a monomeric protein of 525 amino acids (58.1 kDa). The enzyme has a nutritional function in bacteria where it is exported to the periplasmic space to hydrolyze external nucleotides and UDP‐glucose. Related animal 5′‐nucleotidases are attached to the cell membrane via a GPI anchor and hydrolyze nucleotides as extracellular signaling substances. E. coli 5′‐NT belongs to the calcineurin superfamily of metallophosphatases and contains two divalent metal ions at a distance of about 3.3 Å. One of these metal ions is probably Zn2+ in vivo. However, the Zn2+–Zn2+ form is relatively inactive, whereas good activity is seen in the presence of Mg2+, Mn2+, and Co2+. The protein consists of two domains: a larger N‐terminal domain, which is related to the calcineurin superfamily and contains the two catalytic metal ions and its ligands, and the C‐terminal domain, which bears the substrate specificity pocket that binds the nucleoside moiety of the substrates. Thus, the active site is located at the interface between both domains. In the proposed catalytic mechanism, both metal ions are involved in substrate binding, activation of the nucleophile, and transition‐state stabilization. In addition, a catalytic histidine residue (His117 in E. coli 5′‐NT) is strictly conserved in all enzymes of this superfamily.
3D Structure Fold of the (a) open and (b) closed form of 5′‐NT. (a) In the inactive open form, the substrate ATP is bound to the substrate‐specificity pocket formed by the C‐terminal domain (red); (b) the structure of the closed conformation is shown with the ADP‐analogue inhibitor α,β‐methylene‐ADP. The two conformers are related by a 96° domain rotation around the axis that is shown in blue. The bending residues, which enable the domain movement and do not rotate as rigid domains, are shown in yellow. This figure as well as Figures [Figure 1. Structure of the dimetal center complexed with the β‐methylene‐phosphate ...], [Figure 2. Binding mode of AMPCP at the interface between the ...], and [Figure 5. Superposition of the active site structures of AMPCP (blue) ...] have been prepared using programs MOLSCRIPT and RASTER3D.
3D Structure Fold of the (a) open and (b) closed form of 5′‐NT. (a) In the inactive open form, the substrate ATP is bound to the substrate‐specificity pocket formed by the C‐terminal domain (red); (b) the structure of the closed conformation is shown with the ADP‐analogue inhibitor α,β‐methylene‐ADP. The two conformers are related by a 96° domain rotation around the axis that is shown in blue. The bending residues, which enable the domain movement and do not rotate as rigid domains, are shown in yellow. This figure as well as Figures [Figure 1. Structure of the dimetal center complexed with the β‐methylene‐phosphate ...], [Figure 2. Binding mode of AMPCP at the interface between the ...], and [Figure 5. Superposition of the active site structures of AMPCP (blue) ...] have been prepared using programs MOLSCRIPT and RASTER3D.