Chain Q ( A202 L203 Q204 N205 P236 ),  Chain P ( S51 T52 L203 V235 P236 T237 A238 N239 S284 N287 ),  Chain R ( D50 S51 T52 A202 P236 T237 A238 N239 V240 S284 ),  Chain O ( G201 A202 L203 Q204 N205 P236 )