Proteins tunneling

Balabin, I.A. and Onuchic, J.N. (2000) Dynamically controlled protein tunneling pathes in photosynthetic reaction centers, Science 290, 114- 117. 

Figure 30.31 The SRP targeting cycle, (1) Protein synthesis begins on free ribosomes. (2) After the signal sequence has exited the ribosome, it is bound by the SRP, and protein synthesis halts. (3) The SRP-ribosome complex docks with the SRP receptor in the ER membrane. (4) The SRP and SRP receptor simultaneously hydrolyie bound GlPs. Protein synthesis resumes and the SRP is free to bind another signal sequence, (5) The signal peptidase may remove the signal sequence as it enters the lumen of the ER, (6) Protein synthesis continues as the protein is synthesized directly into the ER. (7) On completion of protein synthesis, the ribosome is released and the protein tunnel in the translocon closes. [After H. Lodish et al. Molecular Cell Biology, 5th ed, (W. H. Freeman and Company. 2004), Fig. 16.6,]...

The pathway model makes a number of key predictions, including (a) a substantial role for hydrogen bond mediation of tunnelling, (b) a difference in mediation characteristics as a function of secondary and tertiary stmcture, (c) an intrinsically nonexponential decay of rate witlr distance, and (d) patlrway specific Trot and cold spots for electron transfer. These predictions have been tested extensively. The most systematic and critical tests are provided witlr mtlrenium-modified proteins, where a syntlretic ET active group cair be attached to the protein aird tire rate of ET via a specific medium stmcture cair be probed (figure C3.2.5). 

A Kuki, PG Wolynes. Electron tunneling paths in proteins. Science 236 1647-1652, 1987. T Ziegler. Approximate density functional theory as a practical tool m molecular energetics and dynamics. Chem Rev 91 651-667, 1991. 

Qiu X, Mistry A, Ammirati MJ et al (2007) Crystal structure of cholesteryl ester transfer protein reveals a long tunnel and four bound lipid molecules. Nat Struct Mol Biol 14 106-113... 

The important criterion thus becomes the ability of the enzyme to distort and thereby reduce barrier width, and not stabilisation of the transition state with concomitant reduction in barrier height (activation energy). We now describe theoretical approaches to enzymatic catalysis that have led to the development of dynamic barrier (width) tunneUing theories for hydrogen transfer. Indeed, enzymatic hydrogen tunnelling can be treated conceptually in a similar way to the well-established quantum theories for electron transfer in proteins. 

The transfer of electrons in proteins by a quantum mechanical tunnelling mechanism is now firmly established. Electron transfer within proteins... 

The only (to the best of our knowledge) theoretical treatment of hydrogen transfer by tunnelling to explicitly recognise the role of protein dynamics, and relate this in turn to the observed kinetic isotope effect, was described by Bruno and Bialek. This approach has been termed vibration-ally enhanced ground state tunnelling theory. A key feature of this theory... 

Scrutton, N. S., Basran, J.. Sutcliffe, M. J. 1999 New insights into enzyme catalysis ground state tunnelling driven by protein dynamics. Eur. f. 

In some cases, small biological redox partner proteins such as heme-containing cytochromes, ferredoxins comprising an iron-sulfur cluster, or azurin with a mononuclear Cu site have been used as natural mediators to facilitate fast electron exchange with enzymes. A specific surface site on the redox protein often complements a region on the enzyme surface, and enables selective docking with a short electron tunneling... 

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