Author/Editor		Welin, Martin; Skovgaard, Tine; Knecht, Wolfgang; Zhu, Chunying; Berenstein, Dvora; Munch-Petersen, Birgitte; Piškur, Jure; Eklund, Hans
Title		Structural basis for the changed substrate specificity of Drosophila melanogaster deoxyribonucleoside kinase mutant N64D
Type		članek
Source		FEBS J
Vol. and No.		Letnik 272, št. 14
Publication year		2005
Volume		str. 3733-42
Language		eng
Abstract		The Drosophila melanogaster deoxyribonucleoside kinase (Dm-dNK) double mutant N45D/N64D was identified during a previous directed evolution study. This mutant enzyme had a decreased activity towards the natural substrates and decreased feedback inhibition with dTTP, whereas the activity with 3'-modified nucleoside analogs like 3'-azidothymidine (AZT) was nearly unchanged. Here, we identify the mutation N64D as being responsible for these changes. Furthermore, we crystallized the mutant enzyme in the presence of one of its substrates, thymidine, and the feedback inhibitor, dTTP. The introduction of the charged Asp residue appears to destabilize the LID region (residues 167-176) of the enzyme by electrostatic repulsion and no hydrogen bond to the 3'-OH is made in the substrate complex by Glu172 of the LID region. This provides a binding space for more bulky 3'-substituents like the azido group in AZT but influences negatively the interactions between Dm-dNK, substrates and feedback inhibitors based on deoxyribose. The detailed picture of the structure-function relationship provides an improved background for future development of novel mutant suicide genes for Dm-dNK-mediated gene therapy.
Descriptors		ANIMALS ASPARAGINE ASPARTIC ACID CRYSTALLOGRAPHY, X-RAY DROSOPHILA MELANOGASTER KINETICS MODELS, MOLECULAR MUTATION PHOSPHOTRANSFERASES (ALCOHOL GROUP ACCEPTOR) PROTEIN STRUCTURE, TERTIARY SUBSTRATE SPECIFICITY THYMINE NUCLEOTIDES