{HEAD ~ The P 1 position} refers to {TAIL ~ the amino acid} which precedes the amino acid residue of the peptide that occupies the P1 pocket 
refers to
{ HEAD ~ The P 1 position } refers to { TAIL ~ the amino acid } which precedes the amino acid residue of the peptide that occupies the P1 pocket
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH