Chain A ( I837 N841 I842 L843 D844 L845 A846 S847 M848 K849 A850 T851 S852 R871 S872 K873 L874 L875 E876 K877 M878 Y889 F911 E921 I922 Y923 V924 M925 D926 A927 N928 A929 R930 L931 V932 Q933 F934 E937 Q1080 G1081 I1082 K1389 )