Newlove Tracey, Konieczka Jay H, Cordes Matthew H J
Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, AZ 85701 USA.
Structure. 2004 Apr;12(4):569-81. doi: 10.1016/j.str.2004.02.024.
We report the solution structure of the Cro protein from bacteriophage P22. Comparisons of its sequence and structure to those of lambda Cro strongly suggest an alpha-to-beta secondary structure switching event during Cro evolution. The folds of P22 Cro and lambda Cro share a three alpha helix fragment comprising the N-terminal half of the domain. However, P22 Cro's C terminus folds as two helices, while lambda Cro's folds as a beta hairpin. The all-alpha fold found for P22 Cro appears to be ancestral, since it also occurs in cI proteins, which are anciently duplicated paralogues of Cro. PSI-BLAST and transitive homology analyses strongly suggest that the sequences of P22 Cro and lambda Cro are globally homologous despite encoding different folds. The alpha+beta fold of lambda Cro therefore likely evolved from its all-alpha ancestor by homologous secondary structure switching, rather than by nonhomologous replacement of both sequence and structure.
我们报道了噬菌体P22的Cro蛋白的溶液结构。将其序列和结构与λ Cro的序列和结构进行比较，强烈表明在Cro进化过程中发生了α到β二级结构转换事件。P22 Cro和λ Cro的折叠共享一个由结构域N端一半组成的三个α螺旋片段。然而，P22 Cro的C端折叠成两个螺旋，而λ Cro的C端折叠成一个β发夹。P22 Cro中发现的全α折叠似乎是祖先型的，因为它也存在于cI蛋白中，cI蛋白是Cro古老的重复旁系同源物。PSI-BLAST和传递同源性分析强烈表明，尽管P22 Cro和λ Cro编码不同的折叠，但它们的序列在整体上是同源的。因此，λ Cro的α+β折叠可能是通过同源二级结构转换从其全α祖先进化而来，而不是通过序列和结构的非同源替换。
