Chain A ( F23 A25 I26 T29 K30 V31 N32 R33 E34 R35 Y36 G37 L38 T39 G40 E42 F43 D104 R105 S108 V109 P112 Y115 Y116 N118 M119 L120 N121 I122 Q123 V192 Y195 K209 I210 S211 K212 R213 Q214 L215 N216 F217 T218 K219 T220 V221 F271 R274 T275 Y276 E277 I278 A281 )