In {TAIL ~ certain embodiments}, X3 is selected from {HEAD ~ D arginine}, D lysine and D histidine 
In { TAIL ~ certain embodiments } , X3 is selected from { HEAD ~ D arginine } , D lysine and D histidine
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH