SHORT PEPTIDES AS TURN ELEMENT FOR NUCLEATING SECONDARY STRUCTURES

?-Sheet consist of extended polypeptide strand (?-strand) connected by a network of hydrogen bonds and occur widely in proteins. Intermolecular interaction between the hydrogen-bonding edges of ?-sheet constitute a fundamental form of biomolecular recognition and are involved in protein quaternary structure, protein-protein interactions, and peptide and protein aggregation. The ?-turn is the simplest loop structure with conformational characteristics determined by residues at two positions (i+1, i+2). The early systematic classification of ?-turns reveals a wide variety of geometries and size of loops. One of the design strategies involved in the use of D-residues to construct tight type ? and type ? turns. The results in literature revealed that the ?-turn sequence and its allowed geometry appear to be crucial in dictating the strands alignment. While the formation of ?-helix bundles do not depend strongly on the structure of the connecting loops, in ?-sheet the function of the loop is crucial; five and four-residues loop sequence influence both the kinetics and thermodynamic of the protein folding. The turn units form folded, hydrogen-bonded structures with the peptide groups and prevent the formation of complex, ill-defined aggregates. References: a),Tatham AS, Hayes L, Shewry PR, Urry DW. . Biochim. Biophys. Acta,. 2001, 96: 187-193. b) Lingin Li, Manoj B. Charati, Kristi L.Kiick;J. Polym. Chem. 20101(8), 1160-1170 c) Lòpez de la Paz M., Goldie K., Zurdo J., Lacrois E., Dobson C.M., Serrano L., PNAS 2002, 99(25) 16052-16057