A novel mechanism underlies caspase-dependent conversion of the dicer ribonuclease into a deoxyribonuclease during apoptosis  

作　　者：Xiao Ge Xiang Zhao Akihisa Nakagawa Xinqi Gong Riley Robert Skeen-Gaar Yong Shi Haipeng Gong Xinquan Wang Ding Xue 

机构地区：[1]School of Life Sciences, Tsinghua University, Beijing 100084, China [2]Department of Molecular, Cellular and Developmental Bi-ology, University of Colorado, Boulder, CO 80309, USA

出　　处：《Cell Research》2014年第2期218-232,共15页细胞研究（英文版）

摘　　要：During C. elegans apoptosis, the dicer ribonuclease （DCR-1） is cleaved by the cell death protease CED-3 to generate a truncated DCR-1 （tDCR-1） with one and a half ribonuclease III （RNase III） domains, converting it into a deoxyribonuclease （DNase） that initiates apoptotic chromosome fragmentation. We performed biochemical and functional analyses to understand this unexpected RNase to DNase conversion. In full-length DCR-1, tDCR-1 DNase activity is suppressed by its N-terminal DCR-1 sequence. However, not all the sequence elements in the N-terminal DCR-1 are required for this suppression. Our deletion analysis reveals that a 20-residue a-helix sequence in DCR-1 appears to define a critical break point for the sequence required for suppressing tDCR-1 DNase activity through a structure-dependent mechanism. Removal of the N-terminal DCR-1 sequence from tDCR-1 activates a DNA-binding activity that also requires the one half RNase IIIa domain, and enables tDCR-1 to process DNA. Consistently, structural modeling of DCR-1 and tDCR-1 suggests that cleavage of DCR-1 by CED^3 may cause a conformational change that allows tDCR-1 to bind and process DNA, and may remove steric hindrance that blocks DNA access to tDCR-1. Moreover, a new DNase can be engineered using different RNase III domains, including the one from bacterial RNase III. Our results indicate that very distantly related RNase III enzymes have the potential to cleave DNA when processed proteolytically or paired with an appropriate partner that facilitates binding to DNA. We suggest the possibility that this phenomenon may be extrapolated to other ribonucleases.

关 键 词：C. elegans dicer ribonuclease DEOXYRIBONUCLEASE CASPASE APOPTOSIS CONVERSION 

分 类 号：Q523[生物学—生物化学] Q255