Ellouze C, Takahashi M, Wittung P, Mortensen K, Schnarr M, Nordén B
Groupe d'Etude Mutagénese et Cancérogénèse, Centre National de la Recherche Scientifique Unité 1342, Orsay, France.
Eur J Biochem. 1995 Oct 15;233(2):579-83. doi: 10.1111/j.1432-1033.1995.579_2.x.
Structural changes of the RecA filament upon binding of cofactors have been investigated by small-angle neutron scattering. Both ATP and ADP increased the helical pitch of the RecA homopolymer, which is observed to be 7 nm in the absence of any cofactor. The binding of ATP altered the pitch to 9 nm, whereas the binding of ADP only produced a pitch of 8.2 nm. The pitch determined for the RecA complex with the ATP analog adenosine 5'-[gamma-thio]triphosphate was similar to that found with ATP. Thus, at least three, somewhat different. RecA helical filamentous structures may form in solution. The binding of DNA to RecA did not alter the pitch significantly, indicating that the cofactor binding is the determining factor for the size of the helical pitch of the RecA filament. We also found that elongation of the helical pitch is a necessary, but not a sufficient condition, for the coprotease activity of RecA. The presence of acetate or glutamate ions is also required. The pitch of the ADP.RecA filament is in agreement with that found in the crystal structure. This correlation indicates that this structure corresponds to that of the ADP.RecA filament in solution, although this is not the species active in recombination.
通过小角中子散射研究了辅因子结合后RecA丝的结构变化。ATP和ADP均增加了RecA同聚物的螺旋间距，在不存在任何辅因子时观察到该间距为7nm。ATP的结合将间距改变为9nm，而ADP的结合仅产生8.2nm的间距。与ATP类似物腺苷5'-[γ-硫代]三磷酸形成的RecA复合物所确定的间距与ATP的相似。因此，溶液中可能形成至少三种略有不同的RecA螺旋丝状结构。DNA与RecA的结合并未显著改变间距，表明辅因子结合是RecA丝螺旋间距大小的决定因素。我们还发现螺旋间距的延长是RecA共蛋白酶活性的必要但非充分条件。还需要乙酸盐或谷氨酸离子的存在。ADP.RecA丝的间距与晶体结构中的一致。这种相关性表明该结构对应于溶液中ADP.RecA丝的结构，尽管这不是重组中的活性物种。
