code: public static Structure getReducedStructure(Structure orig){
  		Structure s = new StructureImpl();
  		s.setPDBHeader(orig.getPDBHeader());
  		for ( Chain c : orig.getChains()){
  
  			Chain c1 = new ChainImpl();
  			c1.setId(c.getId());
  			c1.setName(c.getName());
  			c1.setEntityInfo(c.getEntityInfo());
  			s.addChain(c1);
  
  			for (Group g : c.getAtomGroups()){
  
  				Atom a = null;
  				switch(g.getType()) {
  				case AMINOACID:
  					a = g.getAtom(StructureTools.CA_ATOM_NAME);
  					break;
  				case NUCLEOTIDE:
  					a = g.getAtom(StructureTools.NUCLEOTIDE_REPRESENTATIVE);
  					break;
  				default:
  					//omit group
  				}
  				if ( a != null){
  
  					Group g1 = (Group)g.clone();
  					g1.clearAtoms();
  					g1.addAtom(a);
  					c1.addGroup(g1);
  
  				}
  
  			}
  
  		}
  		return s;
  	}
docs: Reduce a structure to a single-atom representation (e.g. CA atoms)
  
  @param orig
  @return
  @since Biojava 4.1.0