1zm8

From Proteopedia

Revision as of 13:37, 20 March 2008

Apo Crystal structure of Nuclease A from Anabaena sp.

Overview

Nuclease A (NucA) is a nonspecific endonuclease from Anabaena sp. capable of degrading single- and double-stranded DNA and RNA in the presence of divalent metal ions. We have determined the structure of the delta(2-24),D121A mutant of NucA in the presence of Zn2+ and Mn2+ (PDB code 1ZM8). The mutations were introduced to remove the N-terminal signal peptide and to reduce the activity of the nonspecific nuclease, thereby reducing its toxicity to the Escherichia coli expression system. NucA contains a betabeta alpha metal finger motif and a hydrated Mn2+ ion at the active site. Unexpectedly, NucA was found to contain additional metal binding sites approximately 26 A apart from the catalytic metal binding site. A structural comparison between NucA and the closest analog for which structural data exist, the Serratia nuclease, indicates several interesting differences. First, NucA is a monomer rather than a dimer. Second, there is an unexpected structural homology between the N-terminal segments despite a poorly conserved sequence, which in Serratia includes a cysteine bridge thought to play a regulatory role. In addition, although a sequence alignment had suggested that NucA lacks a proposed catalytic residue corresponding to Arg57 in Serratia, the structure determined here indicates that Arg93 in NucA is positioned to fulfill this role. Based on comparison with DNA-bound nuclease structures of the betabeta alpha metal finger nuclease family and available mutational data on NucA, we propose that His124 acts as a catalytic base, and Arg93 participates in the catalysis possibly through stabilization of the transition state.

About this Structure

1ZM8 is a Single protein structure of sequence from Anabaena sp.. Full crystallographic information is available from OCA.

Reference

Structural insights into the mechanism of nuclease A, a betabeta alpha metal nuclease from Anabaena., Ghosh M, Meiss G, Pingoud A, London RE, Pedersen LC, J Biol Chem. 2005 Jul 29;280(30):27990-7. Epub 2005 May 15. PMID:15897201

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