Chain A ( K173 V835 S836 K837 R883 S885 P886 L887 E888 L889 F890 M891 L892 S893 R894 H896 L910 V911 E913 Y914 N917 N918 E920 I922 E926 R927 Y928 Y929 F930 A931 Y932 I933 E951 T952 I953 I954 D955 R956 S957 F958 K959 L960 G961 Q964 R965 I966 Y968 Y971 )