Table 1 Conserved sequence motifs found in EEP domains (labeled I through VI in Fig. 2) and the roles of specific amino acids in two EEP domains of known three-dimensional structure (APE1_Hs_1HD7, ExoIII_Ec_1AKO in Fig. 5–7).
REX1/REX2 | APE1 | EXO III |
|---|---|---|
I. TWN | Asn forms a hydrogen bond to catalytic Asp in motif IV | Asn interacts with 5' phosphate group |
II. QE | Glu coordinates Mg2+ ion | Glu coordinates Mg2 ion |
III. HL | His is substituted by Tyr in APE1 but is the catalytic His in DNase I family | His is substituted by Tyr |
IV. GDFN | Catalytic Asp deprotonates the water molecule; Asn forms a hydrogen bond to scissile phosphate | Asn forms a hydrogen bond to scissile phosphate |
V. GRXD (X is S in REX1 and A in REX2) | Asp forms a hydrogen bond to His in motif VI | Asp forms a hydrogen bond to His in motif VI |
VI. SDH | His forms a hydrogen bond to Asp in motif V and to scissile phosphate | Catalytic His deprotonates the water molecule and forms a hydrogen bond to Asp in motif V |