Steady-state kinetic mechanism of the proline:ubiquinone oxidoreductase activity of proline utilization A (PutA) from Escherichia coli

• Published in: Archives of biochemistry and biophysics Vol. 516; no. 2; pp. 113 - 120
• Main Authors: Moxley, Michael A., Tanner, John J., Becker, Donald F.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-12-2011
• Subjects: Bacterial Proteins - antagonists & inhibitors; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; benzoquinones; crystal structure; enzymes; Escherichia coli; Escherichia coli - enzymology; Escherichia coli Proteins - antagonists & inhibitors; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - metabolism; glutamic acid; Kinetics; Membrane Proteins - antagonists & inhibitors; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Models, Molecular; oxidation; proline; Proline - metabolism; Proline dehydrogenase; Proline:ubiquinone oxidoreductase; Protein Structure, Tertiary; PutA; Quinones - metabolism; Quinones - pharmacology; Solvents; Spectrometry, Fluorescence; Substrate Specificity; Tryptophan - chemistry; ubiquinones; Viscosity; Proline metabolism; PutA; Proline:ubiquinone oxidoreductase; Proline dehydrogenase
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/j.abb.2011.10.011

► PutA displays activity with a variety of ubiquinone analogs. ► PutA catalyzes the proline:ubiquinone reaction via a two-site ping-pong mechanism. ► Kinetic parameters for PutA are not significantly affected by ‘osity. ► Proline and ubiquinone bind at two distinct sites in PutA.
The multifunctional proline utilization A (PutA) flavoenzyme from
Escherichia coli performs the oxidation of proline to glutamate in two catalytic steps using separate proline dehydrogenase (PRODH) and Δ
1-pyrroline-5-carboxylate (P5C) dehydrogenase domains
. In the first reaction, the oxidation of proline is coupled to the reduction of ubiquinone (CoQ) by the PRODH domain, which has a β
8α
8-barrel structure that is conserved in bacterial and eukaryotic PRODH enzymes. The structural requirements of the benzoquinone moiety were examined by steady-state kinetics using CoQ analogs. PutA displayed activity with all the analogs tested; the highest
k
cat/
K
m was obtained with CoQ
2. The kinetic mechanism of the PRODH reaction was investigated use a variety of steady-state approaches. Initial velocity patterns measured using proline and CoQ
1, combined with dead-end and product inhibition studies, suggested a two-site ping-pong mechanism for PutA. The kinetic parameters for PutA were not strongly influenced by solvent viscosity suggesting that diffusive steps do not significantly limit the overall reaction rate. In summary, the kinetic data reported here, along with analysis of the crystal structure data for the PRODH domain, suggest that the proline:ubiquinone oxidoreductase reaction of PutA occurs via a rapid equilibrium ping-pong mechanism with proline and ubiquinone binding at two distinct sites.