Tunneling in Ligand Binding to Heme Proteins

Alberding, N.; Austin, R. H.; Beeson, K.; Chan, S. S.; Eisenstein, L.; Frauenfelder, Hans; Nordlund, T. M.

doi:10.1126/science.1273579

Cited by 127 publications

(57 citation statements)

References 17 publications

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“…When this question is asked by impertinent students, many of those who do computer simulations give the glib answer that most of the atoms in biomolecules are heavy, and so they have a small wavelength, thus they act merely as points in their motion. The simulation experts might also say quantum effects such as tunneling are seen but only in low-temperature cryogenic experiments (4), where owing to the lower velocity of atomic motion the thermal de Broglie wavelengths are larger.…”

Section: Classicism Interruptedmentioning

confidence: 99%

Some quantum weirdness in physiology

Wolynes

2009

Proc. Natl. Acad. Sci. U.S.A.

102

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Section: Classicism Interruptedmentioning

confidence: 99%

Some quantum weirdness in physiology

Wolynes

2009

Proc. Natl. Acad. Sci. U.S.A.

102

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“…with frequency factor A, reference temperature T 0 taken to be 100 K and gas constant R. At very low temperatures, quantummechanical tunneling becomes important (28,29). Therefore, the global nonlinear least-squares fit of this model to the data was limited to the temperature range between 40 and 120 K. Moreover, a deviation from the power-law behavior is apparent at longer times for a minor fraction of the total population.…”

Section: [1]mentioning

confidence: 99%

Ligand binding and protein dynamics in neuroglobin

Kriegl

Bhattacharyya

Nienhaus

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

144

210

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Neuroglobin (Ngb) is a recently discovered protein in vertebrate brain tissue that belongs to the globin family of proteins. It has been implicated in the neuronal response to hypoxia or ischemia, although its physiological role has been hitherto unknown. Ngb is hexacoordinate in the ferrous deoxy form under physiological conditions. To bind exogenous ligands like O2 and CO, the His E7 endogenous ligand is displaced from the sixth coordination. By using infrared spectroscopy and nanosecond time-resolved visible spectroscopy, we have investigated the ligand-binding reaction over a wide temperature range (3-353 K). Multiple, intrinsically heterogeneous distal heme pocket conformations exist in NgbCO. Photolysis at cryogenic temperatures creates a five-coordinate deoxy species with very low geminate-rebinding barriers. The photodissociated CO is observed to migrate within the distal heme pocket even at 20 K. Flash photolysis near physiological temperature (275-353 K) exhibits four sequential kinetic features: (i) geminate rebinding (t < 1 s); (ii) extremely fast bimolecular exogenous ligand binding (10 s < t < 1 ms) with a nontrivial temperature dependence; (iii) endogenous ligand binding (100 s < t < 10 ms), which can be studied by using flash photolysis on deoxy Ngb; and (iv) displacement of the endogenous by the exogenous ligand (10 ms < t < 10 ks). All four processes are markedly nonexponential, suggesting that Ngb fluctuates among different conformations on surprisingly long time scales.G lobins are proteins that bind dioxygen and other small ligands at the central iron of a heme prosthetic group embedded in a highly conserved ␣-helical ''globin'' fold. Hemoglobin (Hb) and myoglobin (Mb) are the most prominent members of this protein family (1). Interrelations among structure, dynamics, and function in globins have been investigated in great detail, most likely more thoroughly than for any other protein family. Mb especially has, for a long time, served as a paradigm in the biological physics of proteins (2, 3).Recently, two new members have joined the globin family, cytoglobin (4) and neuroglobin (Ngb) (5). The latter consists of a single chain of 151 aa. Ngb, which occurs in neurons, has less than 25% sequence identity with Mb or Hb but nevertheless displays all key determinants of the globin fold (6). It has moderate oxygen affinity and seems most closely related to the globin found in the glial cells of the annelid Aphrodite (7). The discovery of a six-coordinate heme in the deoxy form of Ngb (5), with the His E7 side chain occupying the sixth coordination, came somewhat as a surprise because it was believed for a long time that a pentacoordinate heme iron, with a vacant ligandbinding site, was a common characteristic of globins. In recent years, however, hexacoordinate globins also have been isolated from bacteria, unicellular eukaryotes, and plants [nonsymbiotic Hbs, nsHbs (8,9), and truncated Hbs, trHbs (10)]. In these proteins, the exogenous ligand has to compete with an intramolecular side chain for ...

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“…1 and the Fig. 1a of Alberding et al [11]). This experimental procedure can be repeated for different temperatures T .…”

Section: Comparison With Experimental Data and Conclusionmentioning

confidence: 99%

“…According to the extension of the Kramers theory presented here, the escape rate at low temperature is κ(T 0) ∝ exp − 2∆U ω a . The quantum calculation based on the Schrödinger equation is more cumbersome if we want to obtain κ QM (T 0) from the value κ QM (T ) obtained at an arbitrary temperature T (see [11] for instance). This difficulty arises because the quantum system is in a heat bath, and because the potential U(x) is complicated enough (see Fig.…”

Section: Comparison With Experimental Data and Conclusionmentioning

confidence: 99%

See 1 more Smart Citation

Tunneling and the Vacuum Zero-Point Radiation

França¹,

Gomes²,

Parra³

2007

Braz. J. Phys.

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We make a brief review of the Kramers escape rate theory for the probabilistic motion of a particle in a potential well U(x), and under the influence of classical fluctuation forces. The Kramers theory is extended in order to take into account the action of the thermal and zero-point random electromagnetic fields on a charged particle. The result is physically relevant because we get a non null escape rate over the potential barrier at low temperatures (T → 0). It is found that, even if the mean energy is much smaller than the barrier height, the classical particle can escape from the potential well due to the action of the zero-point fluctuating fields. These stochastic effects can be used to give a classical interpretation to some quantum tunneling phenomena. Relevant experimental data are used to illustrate the theoretical results.

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Tunneling in Ligand Binding to Heme Proteins

Cited by 127 publications

References 17 publications

Some quantum weirdness in physiology

Some quantum weirdness in physiology

Ligand binding and protein dynamics in neuroglobin

Tunneling and the Vacuum Zero-Point Radiation

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