PDBsum entry 1qhh

Hydrolase

PDB id: 1qhh

Contents

Protein chains

164 a.a. *

261 a.a. *

102 a.a. *

96 a.a. *

Ligands

ATP

Waters ×94

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Dna binding mediates conformational changes and metal ion coordination in the active site of pcra helicase.

Authors

P.Soultanas, M.S.Dillingham, S.S.Velankar, D.B.Wigley.

Ref.

J Mol Biol, 1999, 290, 137-148. [DOI no: 10.1006/jmbi.1999.2873]

PubMed id

10388562

Abstract

Based upon the crystal structures of PcrA helicase, we have made and characterised mutations in a number of conserved helicase signature motifs around the ATPase active site. We have also determined structures of complexes of wild-type PcrA with ADPNP and of a mutant PcrA complexed with ADPNP and Mn2+. The kinetic and structural data define roles for a number of different residues in and around the ATP binding site. More importantly, our results also show that there are two functionally distinct conformations of ATP in the active site. In one conformation, ATP is hydrolysed poorly whereas in the other (activated) conformation, ATP is hydrolysed much more rapidly. We propose a mechanism to explain how the stimulation of ATPase activity afforded by binding of single-stranded DNA stabilises the activated conformation favouring Mg2+binding and a consequent repositioning of the gamma-phosphate group which promotes ATP hydrolysis. A part of the associated conformational change in the protein forces the side-chain of K37 to vacate the Mg2+binding site, allowing the cation to bind and interact with ATP.

Figure 1.
Figure 1. A stereo Figure showing the amino acid residues that contribute to the ATPase active site in the crystal structure of the substrate complex (Velankar et al., 1999).

Figure 5.
Figure 5. (a) Electron density in the active site region of the soaked complex. (b) Electron density in the active site region of the K37A soaked complex. (c) A stereo Figure showing a superposition of the active sites of the soaked complex (blue), and the K37A soaked complex (red).

The above figures are reprinted by permission from Elsevier: J Mol Biol (1999, 290, 137-148) copyright 1999.