In {TAIL ~ certain embodiments}, X4 is selected from D proline, D arginine and {HEAD ~ D} phenylalanine 
In { TAIL ~ certain embodiments } , X4 is selected from D proline , D arginine and { HEAD ~ D } phenylalanine
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH