A Novel Pro-apoptosis Protein PNAS-4 from Xenopus laevis: Cloning, Expression, Purification, and Polyclonal Antibody Production

---

Fei Yan^1,2#, Meilin Qian^1#, Fan Yang², Feng Cai¹, Zhu Yuan^1,2, Songtao Lai², Xinyu Zhao^1,2, Lantu Gou², Zhongguo Hu^1,2, and Hongxin Deng^2*

¹College of Life Science, Sichuan University, Chengdu, Sichuan 610041, P. R. China

²State Key Laboratory of the Biotherapy and Cancer Center, West China Hospital, West China Medical School, Sichuan University, Guo Xue Xiang, No. 37, Chengdu, Sichuan 610041, P. R. China; fax: (8628) 8516-4060; E-mail: denghongx@yahoo.com.cn

^* To whom correspondence should be addressed.

^# Fei Yan and Meilin Qian contributed equally to this work.

Received December 20, 2006; Revision received February 13, 2007

---

Human PNAS-4 was identified as a novel pro-apoptotic protein in mammalian cells. Here we report the cloning, expression, purification, and antibody production of a PNAS-4 homolog (named xPNAS-4) from Xenopus laevis, an extensively used model organism in exploring gene functions during embryonic development. Recombinant histidine-tagged xPNAS-4 protein was expressed in Escherichia coli as insoluble inclusion bodies. The inclusion bodies were subsequently dissolved in 8 M urea and purified to near homogeneity by Ni²⁺ affinity chromatography. The resulting denatured protein was refolded by stepwise dilution of urea concentration via dialysis. This procedure yielded about 4 mg refolded protein per liter of E. coli culture with a purity of 95%. The purified protein was identified by liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry (LC-ESI-Q-TOF-MS) and used to raise anti-xPNAS-4 polyclonal antibodies that were suitable for detecting the expression of PNAS-4 in X. laevis embryos by Western blotting. The availability of recombinant protein and specific polyclonal antibodies will provide a valuable tool in studying apoptotic mechanisms of this protein. To our knowledge, this is the first report to demonstrate the presence of PNAS-4 in X. laevis.

---

KEY WORDS: xPNAS-4, apoptosis, Escherichia coli, protein purification, antibody production

DOI: 10.1134/S0006297907060107

---