title: A comparative study of recombinant mouse and human apurinic/apyrimidinic endonuclease.
abstract: Mammalian apurinic/apyrimidinic endonuclease (APE1) initiates the repair of abasic sites (AP-sites), which are highly toxic, mutagenic, and implicated in carcinogenesis. Also, reducing the activity of APE1 protein in cancer cells and tumors sensitizes mammalian tumor cells to a variety of laboratory and clinical chemotherapeutic agents. In general, mouse models are used in studies of basic mechanisms of carcinogenesis, as well as pre-clinical studies before transitioning into humans. Human APE1 (hAPE1) has previously been cloned, expressed, and extensively characterized. However, the knowledge regarding the characterization of mouse APE1 (mAPE1) is very limited. Here we have expressed and purified full-length hAPE1 and mAPE1 in and from E. coli to near homogeneity. mAPE1 showed comparable fast reaction kinetics to its human counterpart. Steady-state enzyme kinetics showed an apparent K(m) of 91 nM and k(cat) of 4.2 s(-1) of mAPE1 for the THF cleavage reaction. For hAPE1 apparent K(m) and k(cat) were 82 nM and 3.2 s(-1), respectively, under similar reaction conditions. However, k(cat)/K(m) were in similar range for both APE1s. The optimum pH was in the range of 7.5-8 for both APE1s and had an optimal activity at 50-100 mM KCl, and they showed Mg(2+) dependence and abrogation of activity at high salt. Circular dichroism spectroscopy revealed that increasing the Mg(2+) concentration altered the ratio of "turns" to "β-strands" for both proteins, and this change may be associated with the conformational changes required to achieve an active state. Overall, compared to hAPE1, mAPE1 has higher K(m) and k(cat) values. However, overall results from this study suggest that human and mouse APE1s have mostly similar biochemical and biophysical properties. Thus, the conclusions of mouse studies to elucidate APE1 biology and its role in carcinogenesis may be extrapolated to apply to human biology. This includes the development and validation of effective APE1 inhibitors as chemosensitizers in clinical studies.
authors: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC 20057, USA.
authors: Sanjay
authors: S
authors: Adhikari
authors: Praveen Varma
authors: PV
authors: Manthena
authors: Krishna Kiran
authors: KK
authors: Kota
authors: Soumendra Krishna
authors: SK
authors: Karmahapatra
authors: Gargi
authors: G
authors: Roy
authors: Rahul
authors: R
authors: Saxena
authors: Aykut
authors: A
authors: Uren
authors: Rabindra
authors: R
authors: Roy
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity
chemical_list: D011994:Recombinant Proteins; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase