Chain A ( L2 T3 I5 N6 Y7 I8 L9 S10 S11 Y12 A13 Y14 L15 V62 G63 R66 T87 C160 Y161 L162 S163 Y171 L175 E246 Y249 I250 E252 F253 S254 S255 K256 A257 Q258 I259 I260 L261 V262 S263 C264 M265 Y266 L267 R268 M269 L270 )