Plasma membrane-associated malate dehydrogenase of maize (Zea mays L.) roots: native versus recombinant protein

Area of Science:

• Plant biochemistry
• Molecular biology
• Enzymology

Background:

• Malate dehydrogenase (MDH) is vital for plant development, nutrient uptake, and oxidative stress management.
• Previous studies suggested a plasma membrane-associated MDH in maize (Zea mays L.) roots.

Purpose of the Study:

• To purify and characterize plasma membrane-associated MDH isoenzymes from maize roots.
• To compare membrane-associated MDH with soluble isoenzymes.
• To identify the specific maize MDH and its encoding gene.

Main Methods:

• Purification of MDH isoenzymes from enriched plasma membrane preparations.
• Biochemical characterization (Km, pH optima, pI, molecular masses).
• Mass spectrometry (ESI-QTOF-MS/MS, MALDI-TOF-MS) for protein identification.
• Gene cloning and heterologous expression in Escherichia coli.
• Enzyme kinetics and property comparison of native and recombinant proteins.
• Analysis of thiol groups and disulphide bonds.
• Semiquantitative reverse transcription polymerase chain reaction (RT-PCR) for gene expression analysis.

Main Results:

• Membrane-associated MDH from maize roots has a monomeric molecular mass of 41 kDa, differing from soluble isoenzymes (35 kDa monomers, 70 kDa dimers).
• Similar molecular masses were observed for membrane-associated MDH in cauliflower and spinach.
• Mass spectrometry identified the specific maize MDH, and its gene was cloned and expressed.
• Recombinant and native proteins showed comparable enzyme kinetics and properties.
• Constitutive expression of the plasma membrane-associated MDH gene was confirmed in maize roots.

Conclusions:

• A distinct malate dehydrogenase (MDH) is associated with the plasma membrane in maize roots.
• This membrane-associated MDH is structurally and functionally different from soluble MDH isoenzymes.
• The identified gene is constitutively expressed, suggesting a fundamental role in maize root physiology.