title: Secondary structure switching in Cro protein evolution.
abstract: 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.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, AZ 85701 USA.
authors.forename: Tracey
authors.initials: T
authors.lastname: Newlove
authors.forename: Jay H
authors.initials: JH
authors.lastname: Konieczka
authors.forename: Matthew H J
authors.initials: MH
authors.lastname: Cordes
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000737:chemistry* / Q000235:genetics; D002942:Circular Dichroism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics; D017385:Sequence Homology; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins