Flexible Structures and Ligand Interactions of Tandem Repeats Consisting of Proline,Glycine,Asparagine,Serine,and/or Threonine Rich Oligopeptides in Proteins

摘要

Tandem repeats occur in 14% of all proteins.The repeat unit lengths range from a single amino acid to more than 100 residues and the repeat number is sometimes over 100.Understanding the structures,functions,and evolution of these repeats is a significant goal in both proteomics and genomics.This review summarizes experimental studies addressing structural features of tandem repeats of short oligopeptides that are rich in proline,glycine,asparagine,serine,and/or threonine.The oligopetides include(PGMG)and(PNN)in biomineralization protein(PM27),and(NPNA)in Plasmodium falciparum circumsporozoite protein,(YSPTSPS)in RNA polymerase II,(PHGGGWGQ)in the prion protein,(YGHGGG(N))and(YNHGGG(G))in plant glycine-rich proteins,(PGQGQQ),(PGQGQQGQQ)and(GYYPTSOQQ)of wheat HMW glutenin,(FGGMGGGKGG)in Aequipecten abductin.Spectroscopic studies including NMR and CD indicate that these peptides adopt type I and II beta-turns,polyproline II helices,loop conformations,and random coils.Formation of these structures frequently depends on pH,solvent,temperature and hydration.The loop conformations are sometimes stabilized by cation-pi,CH-pi,and/or amino-aromatic interactions.These observations indicate that many tandem repeats are largely flexible.In addition to generating repeating domains and providing flexible linkers between domains,the tandem repeats of(PHGGGWGQ),(YGHGGG(N))and(YNHGGG(G))and those in titin bind Cu~(2+)ions;whereas,tandem repeats of(NPNA)and those in elastin bind Ca~(2+)ions.The interactions of some tandem repeats with various target proteins probably involve an induced fit.The tandem repeats in tropoelastin,flagelliform silk,wheat HMW glutenin,abductin,titin,and human nucleoporin,nup153,are responsible for elastomeric properties.