Chain A ( E51 T53 F54 M113 S114 V115 E116 R117 Y118 L119 A120 I121 N122 H123 A124 Y125 F126 Y127 S128 H129 C202 N203 V206 C207 A209 L210 L211 M213 H214 F217 M218 R220 T221 D253 F254 R255 R256 R257 R258 S259 F260 R261 R262 I263 A264 G265 A266 E267 I268 Q269 M270 V271 I272 L273 L274 K345 )