title: Alpha plus beta folds revisited: some favoured motifs.
abstract: BACKGROUND
  By performing extensive pairwise structural comparisons, we recently identified a set of unique folds from the Brookhaven protein structure data bank. This analysis revealed considerable similarities between a large subgroup of the alpha+beta folds, which led us to re-examine the types of folds occurring in this class and the nature of the relationships between them.
  
  
  RESULTS
  Two major alpha+beta fold groups can be distinguished. In the first, described as alpha-beta sandwiches because alpha-helices and beta-strands occupy separate and distinct layers, a split beta alpha beta motif recurs frequently. The other group, alpha-beta rolls, contains fewer helices and is more diverse. In these, the beta-sheet has folded or rolled over, providing a cradle for the alpha-helix. A beta beta beta alpha-meander motif is found throughout the alpha+beta class.
  
  
  CONCLUSIONS
  Although many alpha-beta sandwiches have very similar folds, few share common functions and the active sites are distributed over the whole surface of the fold. The ability of the alpha-beta sandwich to accommodate a range of functions suggests that it is a stable fold and one that is able to adapt a number of sites to satisfy different functional requirements. In contrast, amongst the alpha-beta rolls, folds having the same roll type often have common functions.
authors.affiliation: Department of Biochemistry and Molecular Biology, University College, London, UK.
authors.forename: C A
authors.initials: CA
authors.lastname: Orengo
authors.forename: J M
authors.initials: JM
authors.lastname: Thornton
mesh_terms: D000818:Animals; D016208:Databases, Factual; D004798:Enzymes / Q000737:chemistry; D006801:Humans; D008958:Models, Molecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*
chemical_list: D004798:Enzymes; D011506:Proteins