Mimicry by asx- and ST-turns of the four main types of beta-turn in proteins.
Hydrogen-bonded beta-turns in proteins occur in four categories: type I (the most common), type II, type II', and type I'. Asx-turns resemble beta-turns, in that both have an NH. . .OC hydrogen bond forming a ring of 10 atoms. Serine and threonine side chains also commonly form hydrogen-bonded turns, here called ST-turns. Asx-turns and ST-turns can be categorized into four classes, based on side chain rotamers and the conformation of the central turn residue, which are geometrically equivalent to the four types of beta-turns. We propose asx- and ST-turns be named using the type I, II, I', and II' beta-turn nomenclature. Using this, the frequency of occurrence of both asx- and ST-turns is: type II' > type I > type II > type I', whereas for beta-turns it is type I > type II > type I' > type II'. Almost all type II asx-turns occur as a recently described three residue feature named an asx-nest.
Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
William J
WJ
Duddy
J Willem M
JW
Nissink
Frank H
FH
Allen
E James
EJ
Milner-White
D006860:Hydrogen Bonding; D018716:Molecular Mimicry; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D009626:Terminology as Topic
D011506:Proteins