Chain A ( L63 ),  Chain C ( I52 S53 E54 Q55 I56 A57 Q58 A60 A61 K65 P66 L67 A68 P69 G70 S71 ),  Chain B ( Q55 L56 A57 E58 V59 A60 V61 S62 A63 K64 R65 E66 A67 V71 )