Chain A ( V30 R31 E32 V33 I34 Q35 N36 P37 R40 V243 S244 M247 L249 H546 V547 L548 P549 I550 D551 Y552 Y553 F554 I673 F674 L675 N676 V677 L678 E679 A680 I681 E682 P683 G684 K718 W719 A720 K721 A722 L723 P724 F726 R727 Y835 )