Probing the Flexibility of the Bacterial Reaction Center: The Wild-Type Protein Is More Rigid Than Two Site-Specific Mutants

详细信息    查看全文

• 作者：Sophie Sacquin-Mora ; Pierre Sebban ; Valé ; rie Derrien ; Bernhard Frick ; Richard Lavery ; Christiane Alba-Simionesco
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：December 25, 2007
• 年：2007
• 卷：46
• 期：51
• 页码：14960 - 14968
• 全文大小：375K
• 年卷期：v.46,no.51(December 25, 2007)
• ISSN：1520-4995

文摘

Experimental and theoretical studies have stressed the importance of flexibility for proteinfunction. However, more local studies of protein dynamics, using temperature factors from crystallographicdata or elastic models of protein mechanics, suggest that active sites are among the most rigid parts ofproteins. We have used quasielastic neutron scattering to study the native reaction center protein from thepurple bacterium Rhodobacter sphaeroides, over a temperature range of 4-260 K, in parallel with twononfunctional mutants both carrying the mutations L212Glu/L213Asp Ala/Ala (one mutant carrying,in addition, the M249Ala Tyr mutation). The so-called dynamical transition temperature, T_d, remainsthe same for the three proteins around 230 K. Below T_d the mean square displacement, <u²>, and thedynamical structure factor, S(Q,), as measured respectively by backscattering and time-of-flight techniquesare identical. However, we report that above T_d, where anharmonicity and diffusive motions take place,the native protein is more rigid than the two nonfunctional mutants. The higher flexibility of both mutantproteins is demonstrated by either their higher <u²> values or the notable quasielastic broadening of S(Q,)that reveals the diffusive nature of the motions involved. Remarkably, we demonstrate here that in proteins,point genetic mutations may notably affect the overall protein dynamics, and this effect can be quantifiedby neutron scattering. Our results suggest a new direction of investigation for further understanding ofthe relationship between fast dynamics and activity in proteins. Brownian dynamics simulations we havecarried out are consistent with the neutron experiments, suggesting that a rigid core within the nativeprotein is specifically softened by distant point mutations. L212Glu, which is systematically conserved inall photosynthetic bacteria, seems to be one of the key residues that exerts a distant control over therigidity of the core of the protein.