code: public String getProteinSequenceString() {
  
  		if (sequence != null)
  			return sequence.toString();
  
  		StringBuilder builder = new StringBuilder();
  		for (Atom a : reprAtoms)
  			// This method preferred over getChemComp.getOneLetterCode because
  			// it returns always X for Unknown residues
  			builder.append(StructureTools.get1LetterCode(a.getGroup()
  					.getPDBName()));
  
  		return builder.toString();
  	}
docs: Get the protein sequence of the Subunit as String.
  
  @return protein sequence String