Conformational changes in an ultrafast light-driven enzyme determine catalytic activity

• Published in: Nature (London) Vol. 456; no. 7224; pp. 1001 - 1004
• Main Authors: Sytina, Olga A, van Stokkum, Ivo H. M, Alexandre, Maxime T, Groot, Marie Louise, Hunter, C. Neil, Heyes, Derren J, van Grondelle, Rienk
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.12.2008; Nature Publishing Group
• Subjects: Analytical, structural and metabolic biochemistry; Biocatalysis - radiation effects; Biological and medical sciences; Catalysis; Catalytic Domain - radiation effects; Changes; Enzymes; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Humanities and Social Sciences; letter; Light; Models, Molecular; multidisciplinary; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors - chemistry; Oxidoreductases Acting on CH-CH Group Donors - metabolism; Oxidoreductases Acting on CH-CH Group Donors - radiation effects; Protein Conformation - radiation effects; Protons; Science; Science (multidisciplinary); Structure-Activity Relationship; Synechocystis - enzymology; Time Factors; United States; Chlorophyll; Protochlorophyllide reductase; Enzyme; Light; Biosynthesis; Oxidoreductases; Catalyst activity; Conformation
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature07354

The role of conformational changes in explaining the huge catalytic power of enzymes is currently one of the most challenging questions in biology. Although it is now widely regarded that enzymes modulate reaction rates by means of short- and long-range protein motions, it is almost impossible to distinguish between conformational changes and catalysis. We have solved this problem using the chlorophyll biosynthetic enzyme NADPH:protochlorophyllide (Pchlide) oxidoreductase, which catalyses a unique light-driven reaction involving hydride and proton transfers. Here we report that prior excitation of the enzyme-substrate complex with a laser pulse induces a more favourable conformation of the active site, enabling the coupled hydride and proton transfer reactions to occur. This effect, which is triggered during the Pchlide excited-state lifetime and persists on a long timescale, switches the enzyme into an active state characterized by a high rate and quantum yield of formation of a catalytic intermediate. The corresponding spectral changes in the mid-infrared following the absorption of one photon reveal significant conformational changes in the enzyme, illustrating the importance of flexibility and dynamics in the structure of enzymes for their function.