Crystal structures of a template-independent DNA polymerase: murine terminal deoxynucleotidyltransferase.
The crystal structure of the catalytic core of murine terminal deoxynucleotidyltransferase (TdT) at 2.35 A resolution reveals a typical DNA polymerase beta-like fold locked in a closed form. In addition, the structures of two different binary complexes, one with an oligonucleotide primer and the other with an incoming ddATP-Co(2+) complex, show that the substrates and the two divalent ions in the catalytic site are positioned in TdT in a manner similar to that described for the human DNA polymerase beta ternary complex, suggesting a common two metal ions mechanism of nucleotidyl transfer in these two proteins. The inability of TdT to accommodate a template strand can be explained by steric hindrance at the catalytic site caused by a long lariat-like loop, which is absent in DNA polymerase beta. However, displacement of this discriminating loop would be sufficient to unmask a number of evolutionarily conserved residues, which could then interact with a template DNA strand. The present structure can be used to model the recently discovered human polymerase mu, with which it shares 43% sequence identity.
Delarue
M
M
Unité de Biochimie Structurale, URA 2185 du CNRS, Institut Pasteur, 25 rue du Dr Roux, 75015 Paris France. delarue@pasteur.fr
Boulé
J B
JB
Lescar
J
J
Expert-Bezançon
N
N
Jourdan
N
N
Sukumar
N
N
Rougeon
F
F
Papanicolaou
C
C
D000595:Amino Acid Sequence; D000818:Animals; D003460:Crystallization; D004253:DNA Nucleotidylexotransferase / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation
D004253:DNA Nucleotidylexotransferase