Chain A ( A687 L701 S703 L704 N705 L707 G708 E709 R710 Q711 L712 W741 M742 M745 V746 A748 M749 R752 L762 Y763 F764 M780 Q783 C784 M787 I869 A870 E872 L873 H874 F876 T877 L880 F891 M895 I899 )