Chain A ( E21 P22 R23 S24 F25 L26 D27 K28 L29 S30 D31 Y32 Y34 G62 F63 Y64 K65 K66 P67 K68 G69 K71 K72 P73 Y74 N75 P76 P107 S109 A128 K129 S130 L137 S138 A139 I140 L141 Y162 A163 H164 C165 I168 L175 E176 L177 W229 )