Molecular Basis for the high catalytic efficiency of plant FNRs.

MUSUMECI, MATÍAS; CATALANO DUPUY, DANIELA L.; RIAL, DANIELA V; ARAKAKI, ADRIÁN K; CECCARELLI, EDUARDO A

Rosario, Santa Fe. ARGENTINA

Congreso; XLII Reunión Anual de la Sociedad Argentina de investigación en Bioquímica y Biología Molecular (SAIB); 2006

Sociedad Argentina de investigación en Bioquímica y Biología Molecular (SAIB)

FNRs are ubiquitous flavoenzymes that participate in a broadrange of redox metabolic pathways. FNRs consist of twodomains; one involved in the binding of the prosthetic group FADand the other in the binding of NADP+. An aromatic residue (Tyr308 in pea FNR) has been suggested to be responsible for high enzyme catalytic efficiency and is conserved in all plant-type FNRs. Tyr308 stacks coplanar to the re-face of the isoalloxazine moiety making extensive interactions with it. Analysing single or double mutants of aliphatic amino acids facing the other side of this Tyr308 by circular dichroism we observed that all mutants were properly folded. Thermal conformational analysis showed that increasing the amino acid volume decreases the stability of the FNRs mutants. Reducing the amino acid volume produces equally or more stables FNRs than the WT enzyme but, with lower catalytic efficiencies, probably due to an increase of the Y308 - isoalloxazine interaction. Our results exemplify how the evolutionary success of enzyme is a compromise between high activity and high stability and show that in the FNR the volume of some aliphatic amino acids have been evolutively selected to maximize enzyme catalytic efficiency.