We report on the response of reaction center (RC) from Rhodobacter sphaeroides (an archetype of membrane proteins) to the exposure at high temperature. The RCs have been solubilized in aqueous solution of the detergent N,N,-dimethyldodecylamine-N-oxide (LDAO). Changes in the protein conformation have been probed by monitoring the variation in the absorbance of the bacteriochlorine cofactors and modification in the efficiency of energy transfer from tryptophans to cofactors and among the cofactors (through fluorescence measurements). The RC aggregation taking place at high temperature has been investigated by means of dynamic light scattering. Two experimental protocols have been used: i) isothermal kinetics, in which the time evolution of RC after a sudden increase of the temperature is probed; ii) T-scans, in which the RCs are heated at constant rate. The analysis of the results coming from both the experiments indicate that the minimal kinetic scheme requires an equilibrium step and an irreversible process. The irreversible step is characterized by a activation energy of 20514 kJ/mol and is independent from the detergent concentration. Since the temperature dependence of the aggregation rate was found to obeys to the same law, the aggregation process is unfolding-limited. On the other hand, the equilibrium process between the native and a partially unfolded conformations was found to be strongly dependent on the detergent concentration. Increasing the LDAO content from 0.025 wt% to 0.5 wt% decreases the melting temperature from 49°C to 42°C. This corresponds to a sizeable ( 22 kJ/mol at 25°C) destabilization of the native conformation induced by the detergent. The nature of the aggregates formed by the denatured RCs depends on the temperature. For temperature below 60°C compact aggregates are formed while at 60°C the clusters are less dense with a scaling relation between mass and size close to that expected for diffusion-limited aggregation. The aggregates final size of formed at different temperatures indicate the presence of an even number of proteins suggesting that these clusters are formed by aggregation of dimers.
Effect of detergent concentration on the thermal stability of a membrane protein: the case study of bacterial reaction center solubilized by N,N,-dimethyldodecylamine-N-oxide
PALAZZO, Gerardo;
2010-01-01
Abstract
We report on the response of reaction center (RC) from Rhodobacter sphaeroides (an archetype of membrane proteins) to the exposure at high temperature. The RCs have been solubilized in aqueous solution of the detergent N,N,-dimethyldodecylamine-N-oxide (LDAO). Changes in the protein conformation have been probed by monitoring the variation in the absorbance of the bacteriochlorine cofactors and modification in the efficiency of energy transfer from tryptophans to cofactors and among the cofactors (through fluorescence measurements). The RC aggregation taking place at high temperature has been investigated by means of dynamic light scattering. Two experimental protocols have been used: i) isothermal kinetics, in which the time evolution of RC after a sudden increase of the temperature is probed; ii) T-scans, in which the RCs are heated at constant rate. The analysis of the results coming from both the experiments indicate that the minimal kinetic scheme requires an equilibrium step and an irreversible process. The irreversible step is characterized by a activation energy of 20514 kJ/mol and is independent from the detergent concentration. Since the temperature dependence of the aggregation rate was found to obeys to the same law, the aggregation process is unfolding-limited. On the other hand, the equilibrium process between the native and a partially unfolded conformations was found to be strongly dependent on the detergent concentration. Increasing the LDAO content from 0.025 wt% to 0.5 wt% decreases the melting temperature from 49°C to 42°C. This corresponds to a sizeable ( 22 kJ/mol at 25°C) destabilization of the native conformation induced by the detergent. The nature of the aggregates formed by the denatured RCs depends on the temperature. For temperature below 60°C compact aggregates are formed while at 60°C the clusters are less dense with a scaling relation between mass and size close to that expected for diffusion-limited aggregation. The aggregates final size of formed at different temperatures indicate the presence of an even number of proteins suggesting that these clusters are formed by aggregation of dimers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
