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

Abstract

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.

The molecular origin of high DNA-repair efficiency by photolyase

“…In addition to photosynthesis and photosignalling, blue light energy is used as a co-substrate for repairing DNA damage by photolyase with high quantum yield 7,8 . The photoenzyme performs biotransformation with multiple elementary chemical steps 9,10 , and at present it is not known whether the initial ultrafast photoinduced process is the determinant of high efficiency. Thus, a key question in photolyase research is how the enzyme optimizes elementary chemical reactions to achieve the high efficiency and the role of the rate of the initial photoinduced process in achieving high quantum yield.…”

Wagging motion of hydrogen-bonded wire in the excited-state multiple proton transfer process of 7-hydroxyquinoline·(NH3)3 cluster

“…Intermolecular hydrogen bond is a site-specific interaction between hydrogen donor and acceptor molecules, and it plays a fundamental role in photophysics, photochemistry and photobiology [1][2][3][4][5]. Therefore, the nature of hydrogen bond in solution is of particular interest and has been investigated extensively by various experimental and theoretical methods [6][7][8][9][10][11].…”

Excited-State Proton Transfer via Hydrogen-Bonded Acetic Acid (AcOH) Wire for 6-Hydroxyquinoline

“…[20][21][22][23][24][25] The proton exchange between an acid and a base in aqueous solution is detected to proceed by a sequential, von Grotthusstype, proton-hopping mechanism through water bridges. [23][24][25] Furthermore, a mechanism of an excited-state H-atom-transfer reaction along a hydrogen-bonded "wire" has also been proposed and widely studied for the importance in photochemical [26][27][28][29][30][31] and biological [32][33][34][35] processes. Hydrogen bonding in the ground state has been extensively studied by many different experimental and theoretical methods.…”