Chain A ( V21 C24 Y25 F26 Y28 Q32 V56 Q59 C60 V61 N63 C90 S93 Y94 A97 M98 S101 N102 K117 C119 K120 P121 V124 L178 S179 L180 T181 L182 D183 G184 T186 G187 Q190 M193 I208 N209 T249 S250 A251 L252 G253 Q254 S255 F256 I257 F258 T260 V261 G265 P266 L267 T268 C269 S270 I271 T273 T274 R276 K277 )