High-resolution Crystal Structure of a Truncated ColE7 Translocation Domain: Implications for Colicin Transport Across Membranes

 

Yi-Sheng Cheng1, Zhonghao Shi1,2, Lyudmila G. Doudeva1,

Wei-Zen Yang1, Kin-Fu Chak2 and Hanna S. Yuan1,2*

1Institute of Molecular BiologyAcademia Sinica, Taipei, Taiwan ROC

2Institute of Biochemistry National Yang-Ming UniversityTaipei, Taiwan, ROC

 

ColE7 is a nuclease-type colicin released from Escherichia coli to kill sensitive bacterial cells by degrading the nucleic acid molecules in their cytoplasm. ColE7 is classified as one of the group A colicins, since the N-terminal translocation domain (T-domain) of the nuclease-type colicins interact with specific membrane-bound or periplasmic Tol proteins during

protein import. Here, we show that if the N-terminal tail of ColE7 is deleted, ColE7 (residues 63–576) loses its bactericidal activity against E. coli. Moreover, TolB protein interacts directly with the T-domain of ColE7 (residues 1–316), but not with the N-terminal deleted T-domain (residues 60–316), as detected by co-immunoprecipitation experiments, confirming

that the N-terminal tail is required for ColE7 interactions with TolB. The crystal structure of the N-terminal tail deleted ColE7 T-domain was determined by the multi-wavelength anomalous dispersion method at a resolution of 1.7 A ° . The structure of the ColE7 T-domain superimposes well with the T-domain of ColE3 and TR-domain of ColB, a group A

Tol-dependent colicin and a group B TonB-dependent colicin, respectively. The structural resemblance of group A and B colicins implies that the two groups of colicins may share a mechanistic connection during cellular import.

q 2005 Elsevier Ltd. All rights reserved.

 

Keywords: protein cellular import; membrane translocation; colicin

structure; colicin translocation domain; crystal structu

 

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