Chain A ( Q71 I72 V73 S74 F75 Y76 K78 L79 N82 L118 T119 N120 Y121 S122 V123 ),  Chain B ( Q71 I72 V73 S74 F75 Y76 F77 K78 L79 N82 F115 K117 L118 T119 N120 Y121 S122 V123 )