Chain A ( R562 Y571 T574 L575 I577 S578 M579 C581 S582 K583 T584 F585 D588 S589 N590 K591 R592 G602 A603 D604 L605 E606 K607 Y608 F609 Y610 G611 E612 I613 A614 L616 Y633 L636 N637 S638 T642 K643 Y644 Y645 F647 E806 D807 R808 P809 S810 T811 R812 N813 F814 ), Chain B ( N42 Y43 F44 L45 Q46 I47 S48 R49 V50 N51 D52 L53 R55 I117 K118 S119 T124 Y257 H260 Y264 )