Protein dynamics and their functional activity

Photosensitive systems are convenient objects for analysing a possible correlation between the dynamic and functional properties of proteins. After a short light pulse, it is possible to observe a chemical reaction and to trace the dynamical state of the matrix with the aid of internal and external physical labels. 

The dynamic state of sperm-whale myoglobin monitored by spin, fluorescence, and Mossbauer labels (Likhtenshtein, 1988, 1993) as a function of temperature was compared with the results ofkinetic studies on the photodissociation and reassociation of CO-deoxymyoglobin (Frauenfelder et al, 1991). The three independent labelling methods showed sharp increases in nanosecond mobility in the vicinity of the label in a temperature region of approximately 200-220 K. These temperatures were close to the temperatures of the dramatic increases in the relative quantum yield of the photodissociation, as well as to the fraction of non-dissociated molecules for 10 2 s 

A detailed investigation of the possible role of media (protein and membrane) dynamics in electron transfer was carried out on the reaction centre (RC) extracted from Rhodopseudomonas spheroidas in the isolated state and in the composition of the photosynthetic membrane (Berg et al., 1979a, b Likhtenshtein, 1979a, b Likhtenshtein et al., 1979 Kotelnikov et al., 1983 Kochetkov et al., 1984 Parak et al., 1983 Knox, 1989 Likhtenshtein, 1988(a, b), 1993, 1996 Likhtenshtein et al., 2000). 

Mossbauer, fluorescent and phosphorescent labels were introduced into the various portions of the system being studied. They were covalently bound to the RC surface groups, adsorbed by the hydrophobic segments of the protein and membrane, and 57Fe atoms were incorporated by way of biosynthesis into iron-containing proteins. Then, in the same samples, the dependence on temperature, moisture content and viscosity was measured for the label mobility and the rate constant of electron transfer 

Very fast electron transfers from P+ to bacteriochlorophyl (Bchl) and from (Bchl)- to QA do not depend on media dynamics and occur via conformationally non-equilibrium states (Fig.3.18). The dual fluorophore-nitroxide molecules (D-A) are also convenient objects for analysing the activity-dynamics relationship. The marked irreversible photoreduction of the nitroxide fragment of the dual probe incorporated into the binding site of HSA only took place when the nanosecond dynamical processes around the probe traced by ESR and fluorescence methods were detected (Rubtsova et al., 1993, Fogel et al, 1994 Likhtenshtein, 1986 Lozinsky et al., 2002). Similar results were reported for another model protein system, i.e. a-chymotrypsin with spin labeled methionin-92 groups (Belonogova et al., 1997). In the latter enzyme, the excited tryptophan group serves as an electron donor. 

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