CRYSTAL STRUCTURES OF PEPTIDES DESIGNED TO MIMIC PROTEIN SECONDARY STRUCTURAL ELEMENTS K. R. Rajashankar, S. Ramakumar, V. S. Chauhan, Department of Physics, Indian Institute of Science, Bangalore, India and ICGEB, Aruna Asaf Ali Marg, New Delhi, India

Peptides containing a,ß-dehydroamino acid residues are found to exhibit specific conformational preference and altered biological activity. They are found in many naturally occurring peptides and proteins of microbial and fungal origin. In particular, a,ß-dehydro phenylalanine ([[Delta]]Phe), has become one of the most promising conformation restricting residue useful in peptide design. Theoretical and experimental studies on oligopeptides containing [[Delta]]Phe residues have demonstrated the potential of [[Delta]]Phe residues to induce folded conformation. In order to understand the effect of the number and relative positioning of [[Delta]]Phe residues on the overall conformation of peptide sequences, we have carried out a systematic study of a number of peptides containing [[Delta]]Phe residue/s. In this paper crystal structure of nine peptides containing [[Delta]]Phe residue/s will be discussed, highlighting the utility of [[Delta]]Phe as a `designer residue'. The sequence and conformation of the peptides studied are listed in the table below.

   Peptide Sequence                           Conformation   
1  Boc0-Val1- [[Delta]]Phe2-Phe3-Ala4-Phe5-   TR             
   [[Delta]]Phe6-Val7-                                       
   [[Delta]]Phe8-Gly9-OMe                                    
2  Boc0-Leu1-Phe2-Ala3-                       TR             
   [[Delta]]Phe4-Leu5-OMe                                    
3  Boc0-Leu1- [[Delta]]Phe2-                  TR             
   [[Delta]]Phe3-Ala4-Phe5-NHMe                              
4  Boc0-Val1- [[Delta]]Phe2- [[Delta]]Phe3-   TL             
   [[Delta]]Phe4-Val5-OMe                                    
5  Boc0-Val1-                                 AR             
   [[Delta]]Phe2-Ala3-Leu4-Gly5-OMe                          
6  Boc0-Pro1- [[Delta]]Phe2-Ala3-             B              
   [[Delta]]Phe4-Ala5-OMe                                    
7  Boc0-Val1- [[Delta]]Phe2-Leu3-Phe4-Ala5-   TRS            
   [[Delta]]Phe6-Leu7-OMe                                    
8  Boc0-Val1-                                 TRS            
   [[Delta]]Phe2-Phe3-Ala4-Leu5-Ala6-                        
   [[Delta]]Phe7-Leu8-OMe                                    
9  Ac0- [[Delta]]Phe1-Val2-                   A/TRS          
   [[Delta]]Phe3-Phe4-Ala5-Val6-                             
   [[Delta]]Phe7-Gly8-OMe