{HEAD ~ The P5 position} refers to {TAIL ~ the amino acid residue} that follows the amino acid residue that occupies the P4 pocket 
refers to
{ HEAD ~ The P5 position } refers to { TAIL ~ the amino acid residue } that follows the amino acid residue that occupies the P4 pocket
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH