Three Different and Tissue-specific NAD-Malic Enzymes Generated by Alternative Subunit Association in Arabidopsis thaliana

TRONCONI, MARCOS. A; MAURINO, VERONICA. G; ANDREO CARLOS S. AND DRINCOVICH MARIA. F

JOURNAL OF BIOLOGICAL CHEMISTRY

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

Año: 2010 vol. 285 p. 11870 - 11879

0021-9258

The Arabidopsis thaliana genome contains two genes encodingthe mitochondrial NAD-malic enzyme (NAD-ME), NADME1(At2g13560) and NAD-ME2 (At4g00570). The characterizationof recombinant NAD-ME1 and -2 indicated that bothenzymes assemble as active homodimers; however, a heterodimericenzyme (NAD-MEH) can also be detected by electrophoreticstudies. To analyze the metabolic contribution ofeach enzymatic entity, NAD-MEH was obtained by a co-expression-based recombinant approach, and its kinetic and regulatoryproperties were analyzed. The three NAD-MEs show similarkinetic properties, although they differ in the regulation byseveral metabolic effectors. In this regard, whereas fumarateactivates NAD-ME1 and CoA activates NAD-ME2, both compoundsact synergistically on NAD-MEH activity. The characterizationof two chimeric enzymes between NAD-ME1 and -2allowed specific domains of the primary structure, which areinvolved in the differential allosteric regulation, to be identified.NAD-ME1and -2 subunits showed a distinct pattern of accumulationin the separate components of the floral organ. In sepals,the NAD-ME1 subunit is present at a slightly higher proportionthan the NAD-ME2 subunit, and thus, NAD-MEH and NADME1act in concert in this tissue. On the other hand, NAD-ME2is the only isoform present in anthers. In view of the differentproperties of NAD-ME1, -2, and -H, we suggest that mitochondrialNAD-ME activity may be regulated by varying native associationin vivo, rendering enzymatic entities with distinct allostericregulation to fulfill specific roles. The presence of threedifferent NAD-ME entities, which originate by alternative associationsof two subunits, is suggested to be a novel phenomenonunique to plant mitochondria.