RESIDUE   CUK      6
CONECT      S1     4 CU1  CU2  CU3  CU4 
CONECT      CU1    2 S1   S2  
CONECT      S2     2 CU1  CU4 
CONECT      CU2    1 S1  
CONECT      CU3    1 S1  
CONECT      CU4    2 S1   S2  
END   
HET    CUK              6
HETNAM     CUK [4Cu:2S] cluster
FORMUL      CUK    Cu4 S2