3QAL: Crystal Structure Of Arg280ala Mutant Of Catalytic Subunit Of Camp- Dependent Protein Kinase

Eukaryotic protein kinases (EPKs) feature two coevolved structural segments, the Activation segment, which starts with the Asp-Phe-Gly (DFG) and ends with the Ala-Pro-Glu (APE) motifs, and the helical GHI subdomain that comprises alphaG-alphaH-alphaI helices. Eukaryotic-like kinases have a much shorter Activation segment and lack the GHI subdomain. They thus lack the conserved salt bridge interaction between the APE Glu and an Arg from the GHI subdomain, a hallmark signature of EPKs. Although the conservation of this salt bridge in EPKs is well known and its implication in diseases has been illustrated by polymorphism analysis, its function has not been carefully studied. In this work, we use murine cAMP-dependent protein kinase (protein kinase A) as the model enzyme (Glu208 and Arg280) to examine the role of these two residues. We showed that Ala replacement of either residue caused a 40- to 120-fold decrease in catalytic efficiency of the enzyme due to an increase in K(m)(ATP) and a decrease in k(cat). Crystal structures, as well as solution studies, also demonstrate that this ion pair contributes to the hydrophobic network and stability of the enzyme. We show that mutation of either Glu or Arg to Ala renders both mutant proteins less effective substrates for upstream kinase phosphoinositide-dependent kinase 1. We propose that the Glu208-Arg280 pair serves as a center hub of connectivity between these two structurally conserved elements in EPKs. Mutations of either residue disrupt communication not only between the two segments but also within the rest of the molecule, leading to altered catalytic activity and enzyme regulation.
PDB ID: 3QALDownload
MMDB ID: 95514
PDB Deposition Date: 2011/1/11
Updated in MMDB: 2011/12
Experimental Method:
x-ray diffraction
Resolution: 1.7  Å
Source Organism:
synthetic construct
Similar Structures:
Biological Unit for 3QAL: dimeric; determined by author and by software (PISA)
Molecular Components in 3QAL
Label Count Molecule
Proteins (2 molecules)
Camp-dependent Protein Kinase Catalytic Subunit Alpha(Gene symbol: Prkaca)
Molecule annotation
Protein Kinase Inhibitor
Molecule annotation
Chemicals (3 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB