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Something known to cut is doing the jointing job


The bacterial pathogen Legionella pneumophila injects hundreds of virulence factors into host cell to tame its defense. SidC is one such factor that had been extensively studied. This protein is important for membrane remodeling of the bacterial phagosome and for its recruitment of ubiquitin conjugates. However, the biochemical function of this protein remains elusive. Together with Dr. Yuxin Mao's group at Cornell University, postdoctoral associate Jiazhang Qiu and Zhao-Qing Luo revealed that this protein is a novel ubiquitin ligase. Ubiquitin ligases normally only exist in eukaryotic cells; they function to add a 76-residue ubiquitous protein (thus called ubiquitin) to other proteins, often leading to their degradation or change of activity. Adding of ubiquitin to other proteins by SidC requires a structure made of three amino acids, cysteine (C), histidine (H) and aspartic acid (D) (CHD) (Figure). When the ligase activity was abolished by mutation, SidC completely lost its ability in aiding the bacterium in infection. The CHD structure is present in many proteins and it is known to destroy proteins or to remove ubiquitin from proteins. This discovery not only assigned a completely new role to a common structure, but also laid the foundation for establishing potentially novel linkages between ubiquitination and membrane trafficking, a cellular event involved in many diseases, including infection.

FoSheng Hsu, Xi Luo, Jiazhang Qiu, Yan-Bin Teng, Jianping Jin,, Marcus B. Smolka,, Zhao-Qing Luo, and Yuxin Mao, 2014. The Legionella effector SidC defines a unique family of ubiquitin ligases important for bacterial phagosomal remodeling. Proc. Natl. Acad. Sci. USA. Jul 8. pii: 201402605.

Article and photo provided by Zhao-Qing Luo, Associate Professor of Biological Sciences.

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