Chain A ( L254 D255 S256 E257 D258 Y259 S260 L261 S262 E263 E264 G265 Q266 E267 L268 S269 P437 C438 V439 I440 C441 Q442 G443 R444 P445 K446 N447 G448 C449 I450 V451 H452 G456 H457 L458 M459 A460 C461 F462 T463 C464 A465 K466 K467 L468 K469 K470 R471 N472 K473 P474 C475 P476 V477 C478 I482 Q483 M484 I485 )