Chain A ( R124 H127 V130 V131 P132 Y163 M164 R166 I167 S168 T169 R170 M171 L172 M173 N174 S193 Y243 V244 P245 S246 H247 L248 H249 H250 M251 L252 F253 E254 L255 Y309 G333 I336 S337 L339 Y340 Y343 F344 E373 )