Destabilization of the homotetrameric assembly of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase from the hyperthermophile Pyrococcus furiosus enhances enzymatic activity.
Many proteins adopt homomeric quaternary structures to support their biological function, including the first enzyme of the shikimate pathway that is ultimately responsible for the biosynthesis of the aromatic amino acids in plants and microorganisms. This enzyme, 3-deoxy-d-arabino-heptulosonate-7-phosphate synthase (DAH7PS), adopts a variety of different quaternary structures depending on the organism in which it is found. The DAH7PS from the hyperthermophilic archaebacterium Pyrococcus furiosus was previously shown to be tetrameric in its crystalline form, and this quaternary association is confirmed in an improved structure in a different crystal system. This tetramer is also present in solution as revealed by small-angle X-ray scattering and analytical ultracentrifugation. This homotetrameric form has two distinct interfaces, both of which bury over 10% each of the surface area of a single monomer. Substitution of Ile for Asp in the hydrophobic region of one interface gives a protein with a remarkable 4-fold higher maximum catalytic rate than the wild-type enzyme. Analytical ultracentrifugation at pH7.5 reveals that the tetrameric form is destabilized; although the protein crystallizes as a tetramer, equilibrium exists between tetrameric and dimeric forms with a dissociation constant of 22 μM. Thus, under the conditions of kinetic assay, the enzyme is primarily dimeric, revealing that the dimeric form is a fully functional catalyst. However, in comparison to the wild-type protein, the thermal stability of the dimeric protein is significantly compromised. Thus, an unusual compromise of enzymatic activity versus stability is observed for this DAH7PS from an organism that favors a hyperthermophilic environment.
Biomolecular Interaction Centre and Department of Chemistry, University of Canterbury, PO Box 4800, Christchurch 8140, New Zealand.
Ali Reza
AR
Nazmi
Institute of Fundamental Sciences, Massey University, PO Box 11-222, Palmerston North 4442, New Zealand.
Linley R
LR
Schofield
Biomolecular Interaction Centre and School of Biological Sciences, University of Canterbury, PO Box 4800, Christchurch 8140, New Zealand; Bio21 Molecular Science and Biotechnology Institute, Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3010, Australia.
Renwick C J
RC
Dobson
Institute of Fundamental Sciences, Massey University, PO Box 11-222, Palmerston North 4442, New Zealand.
Geoffrey B
GB
Jameson
Biomolecular Interaction Centre and Department of Chemistry, University of Canterbury, PO Box 4800, Christchurch 8140, New Zealand. Electronic address: emily.parker@canterbury.ac.nz.
Emily J
EJ
Parker
D010723:3-Deoxy-7-Phosphoheptulonate Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002850:Chromatography, Gel; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D020027:Pyrococcus furiosus / Q000201:enzymology*; D053838:Scattering, Small Angle
D050505:Mutant Proteins; D010723:3-Deoxy-7-Phosphoheptulonate Synthase
3-deoxy-d-arabino-heptulosonate-7-phosphate synthase; DSC; DSF; PEG; SAXS; analytical ultracentrifugation; differential scanning calorimetry; differential scanning fluorimetry; mutagenesis; polyethylene glycol; quaternary structure; shikimate pathway; small-angle X-ray scattering