SHORT BIOACTIVE PEPTIDES AS TURN AND LOOP

?Beta-sheet consist of extended polypeptide strand (beta-strand) connected by a network of hydrogen bonds and occur widely in proteins. Intermolecular interaction between the hydrogen-bonding edges of beta-sheet constitute a fundamental form of biomolecular recognition (like DNA base pairing) and are involved protein quaternary structure, protein-protein interactions, and peptide and protein aggregation. The beta-turn is the simplest loop structure with conformational characteristics determined by residues at two positions (i+1, i+2). The early systematic classification of beta-turns reveals a wide variety of geometries and size of loop. One of the design strategies involved in the use of D-residues to construct tight type I' and type II' turns. The results in literature revealed that the beta-turn sequence and its allowed geometry appear to be crucial in dictating the strands alignment. While the formation of ?-helical bundles do not depend strongly on the structure of the connecting loops, in beta-sheet formation the function of the loop is crucial; five and four-residues loop 1 sequences influence both the kinetics and thermodynamic of the protein folding.