title: Structural motifs are closed into cycles in proteins.
abstract: Beta-hairpins, triple-strand beta-sheets and betaalphabeta-units represent simple structural motifs closed into cycles by systems of hydrogen bonds. Secondary closing of these simple motifs into large cycles by means of different superhelices, split beta-hairpins or SS-bridges results in the formation of more complex structural motifs having unique overall folds and unique handedness such as abcd-units, phi-motifs, five- and seven-segment alpha/beta-motifs. Apparently, the complex structural motifs are more cooperative and stable and this may be one of the main reasons of high frequencies of occurrence of the motifs in proteins.
authors.affiliation: Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russian Federation. efimov@protres.ru
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Efimov
mesh_terms: D020816:Amino Acid Motifs; D006860:Hydrogen Bonding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*
chemical_list: D011506:Proteins