Ultrafast Short-range

Electron Transfer Dynamics in Biology

Ting-Fang He

Programs of Ohio State Biochemistry, Biophysics, and Chemical Physics, and

Departments of Physics, Chemistry, and Biochemistry, The Ohio State University,

Columbus, Ohio 43210

Dr. Dongping Zhong

Biology

ELECTRON TRANSFER

ChemistryPhysics

Signal transduction

Phosphorylation

Dephosphorylation

Proton translocation

Cell respiratory chain

Energy conversion processes

Oxidation; reduction

Organic synthesis

Solid-state physics

Surface physics

Current Opinion in Chemical Biology 2007, 11:174–181

DNA repair

Biology Electron Transfer

Photosynthesis Phototrop

ism DNA repair, etc.

light

Cold Spring Harbor Laboratory Press: Cold Spring Harbor, NY (2007). 

Flavodoxin (D. Vulgaris)

At short range, how does protein steer electron transfer dynamics by

coupling with the active-site motions ?

Ultrafast Electron Transfer Dynamics

Redox bacterial proteins.

Act as an electron shuttle.

Sulfite-reducing system; Nitrogen fixation.

light

e-

e-

Electron Transfer

A* D D+

DA

A-kET

kBACK ET

hν

J. Phys. Chem. B, Vol. 108, No. 46, 2004

fs

ps ns µs

Upper-limit electron transfer dynamics at the tunneling distances in protein

20 Ǻ

10 Ǻ

15 Ǻ

5 ǺClose contact

Nuclear motion in protein

400 nm

τBACK ET ~ 1.5 ps

λ probe 490 nm

τBACK ET ~ 1.5 ps

λ probe 580 nm

-1 0 1 2 3 4 5 6 7 8 9 10 11 12

time/ ps

λ flu 530 nm

τET ~ 0.4 ps

τBACK ET

e-

e-

τET

FMN* Trp Trp+

TrpFMN

FMN-

kET

kBACK ET

ResultResultss

Flavodoxin Y98F

0 3 6 9 12 15

λ probe 540 nm

λ probe 510 nm

λ probe 518 nm

λ probe 525 nm

λ probe 560 nm

time/ ps

ResultResultss

320 360 400 440 480 520 560

wavelength (nm)

Flavodoxin Y98F

400 nm

1.5 ps

4.5 ps

Electron Transfer Coordinate

ultrafast forward electron transfer

Trp+

FMN-

Trp

FMN*

Trp

FMN400 nm

Solvation plus back electron transfer

e-

kET

kBACK ET

ResultResultss

320 360 400 440 480 520 560

wavelength (nm)

Flavodoxin W60F

e-

0 3 6 9 12 15time/ ps

λ probe 540 nm

λ probe 500 nm

λ probe 510 nm

λ probe 525 nm

400 nm 3.6 ps

0 3 6 9 12 15time/ ps

λ probe 560 nm

λ probe 500 nm

λ probe 510 nm

λ probe 525 nm

λ probe 518 nm

320 360 400 440 480 520 560

wavelength (nm)

Flavodoxin wild type

ResultResultss e-

e-

kET

kBACK ET

400 nm

1.5 ps

5 ps

ConcluConclusionsion

(b) The back electron transfer turns out being more than two times slower than its forward, ~1.5 ps.

(c) The recombination process is found at the hot ground state before the redox molecules and the protein solvents relax vibrationally to the equilibrated configurations.

How universal in regulating the biological function?

(d) The subsequent vibrational relaxation (cooling) is determined ~5 ps in the active-site pocket.

(e) The study indicates that, for the highly exergonic back electron transfer (the inverted region), at this short range, there appears a hot channel at the vibrational excited electronic ground state to boost the return dynamics.

(a) Under the oxidized flavodoxin, the forward electron transfer dynamics from the van der Waals contact aromatic amino acids to the excited flavin is determined faster than 0.5 ps.

AcknowledgAcknowledgements ements

Group MembersQing DingDr. Xunmin GuoAli HassanaliDr. Jiang LiTangping LiZheyun LiuJingwei LuJustin LinkOseoghaghare OkobiahWeihong QiuJeff StevensChuang TanYi YangChen ZangLuyuan Zhang

the National Institutes of Health the Packard Foundation Fellowship

Funding

AdvisorDr. Dongping Zhong

Professor Richard P. Swenson

CoworkersLijuan WangDr. Lijun GuoDr. Chaitanya Saxena Ya-Ting Kao