Chain A ( I249 A250 C251 I252 G253 G254 M331 H332 P333 D334 R335 P336 V338 M470 P471 N472 A473 W474 A475 L478 V507 S509 W510 Q511 F512 S513 S514 T515 T516 R518 W562 D566 I568 I569 D570 K573 K574 )