Doctor of Philosophy (PhD)


Biological Sciences

Document Type



The increase in environmental pollution urges us to find alternative sources and materials to decrease it in order to preserve the human societies on Earth. The molecule 3-hydroxypropionic acid is a versatile crucial industrial chemical that is a precursor to bioplastic, poly(3-hydroxypropionic acid), among other chemicals. The 3-hydroxypropionic acid biosynthesis is achieved in recombinant microorganisms via the malonyl-CoA pathway catalyzed by the cornerstone enzyme, malonyl-CoA reductase in two separate reactions using NADPH. The conversion of malonyl-CoA to malonic semialdehyde is completed in the C-terminal part of malonyl-CoA reductase. The subsequent reduction of malonic semialdehyde to 3-hydroxypropionic acid is accomplished in the N-terminal part of malonyl-CoA reductase. Malonyl-CoA reductase belongs to the short chain dehydrogenases/reductases family and both halves have a characteristic catalytic triad, Ser-Tyr-Lys in the C-terminal part, and Thr-Tyr-Lys in the N-terminal part of the malonyl-CoA reductase. In this work, the plasmid constructs for both halves of malonyl-CoA reductase were prepared, and proteins were expressed separately and characterized kinetically. The C-terminal half demonstrated a step wise mechanism in which the conformational changes from the ordered binding of the substrates, NADPH followed by malonyl-CoA, in a pH-dependent step, precede the hydride transfer in which the sidechains of both tyrosine and serine stabilize the oxyanion in the transitional state facilitating the pro-S hydride transfer by making C-O bond more polar. On the other hand, the N-terminal half revealed random binding of substrates NADP+ and 3-hydroxypropionic acid with NADP+ preferentially binding first, and a concerted mechanism where proton transfer to the catalytic tyrosine and the hydride transfer to NADP+ occur simultaneously.

In conclusion, the major findings include different kinetic mechanisms for both halves of malonyl-CoA reductase. The stepwise mechanism was revealed for the C-terminal part of malonyl-CoA with tyrosine that has no general acid/base role, and the concerted mechanism was elucidated for the N-terminal part of malonyl-CoA where tyrosine has a general acid/base role.



Committee Chair

Waldrop, Grover L.

Available for download on Thursday, December 31, 2026

Included in

Biochemistry Commons