Chain A ( P12 M13 F14 S15 G16 K17 S18 T19 E20 L21 I22 R23 K39 Y40 D43 R45 Y46 G47 S49 V50 Y51 T52 H53 D54 N55 N56 D82 E83 Q85 F86 F87 A107 L109 L134 L159 I160 G161 G162 K163 )