Restructuring of the dinucleotide-binding fold in an NADP(H) sensor protein.
NAD(P) has long been known as an essential energy-carrying molecule in cells. Recent data, however, indicate that NAD(P) also plays critical signaling roles in regulating cellular functions. The crystal structure of a human protein, HSCARG, with functions previously unknown, has been determined to 2.4-A resolution. The structure reveals that HSCARG can form an asymmetrical dimer with one subunit occupied by one NADP molecule and the other empty. Restructuring of its NAD(P)-binding Rossmann fold upon NADP binding changes an extended loop to an alpha-helix to restore the integrity of the Rossmann fold. The previously unobserved restructuring suggests that HSCARG may assume a resting state when the level of NADP(H) is normal within the cell. When the NADP(H) level passes a threshold, an extensive restructuring of HSCARG would result in the activation of its regulatory functions. Immunofluorescent imaging shows that HSCARG redistributes from being associated with intermediate filaments in the resting state to being dispersed in the nucleus and the cytoplasm. The structural change of HSCARG upon NADP(H) binding could be a new regulatory mechanism that responds only to a significant change of NADP(H) levels. One of the functions regulated by HSCARG may be argininosuccinate synthetase that is involved in NO synthesis.
Zheng
Xiaofeng
X
National Laboratory of Protein Engineering and Plant Genetic Engineering, Department of Biochemistry and Molecular Biology, College of Life Sciences, Peking University, Beijing 100871, China. xiaofengz@pku.edu.cn
Dai
Xueyu
X
Zhao
Yanmei
Y
Chen
Qiang
Q
Lu
Fei
F
Yao
Deqiang
D
Yu
Quan
Q
Liu
Xinping
X
Zhang
Chuanmao
C
Gu
Xiaocheng
X
Luo
Ming
M
D001665:Binding Sites; D018360:Crystallography, X-Ray; D003687:Dehydroepiandrosterone; D006367:HeLa Cells; D006801:Humans; D006860:Hydrogen Bonding; D009249:NADP / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*
C520476:NMRAL1 protein, human; D014157:Transcription Factors; D003687:Dehydroepiandrosterone; D009249:NADP