Chain B ( M49 W50 D71 V72 K73 K74 D75 L76 E86 G87 E88 G114 L115 F116 K117 T118 N119 T120 G121 T122 I123 G124 A125 V126 S137 I139 V146 V147 G148 L149 Y150 G151 N152 G153 V154 V155 T156 R157 A160 V162 S163 A164 I165 A166 N167 )