Download MendeleyCrystal structure of theStreptococcus agalactiaeCAMP factor provides insights into its membrane-permeabilizing activity.
Jin, T., Brefo-Mensah, E., Fan, W., Zeng, W., Li, Y., Zhang, Y., Palmer, M.(2018) J Biol Chem 293: 11867-11877
- PubMed: 29884770
- DOI: https://doi.org/10.1074/jbc.RA118.002336
- Primary Citation of Related Structures:
5H6I - PubMed Abstract:
Streptococcus agalactiae is an important human opportunistic pathogen that can cause serious health problems, particularly among newborns and older individuals. S. agalactiae contains the CAMP factor, a pore-forming toxin first identified in this bacterium. The CAMP reaction is based on the co-hemolytic activity of the CAMP factor and is commonly used to identify S. agalactiae in the clinic. Closely related proteins are present also in other Gram-positive pathogens. Although the CAMP toxin was discovered more than a half century ago, no structure from this toxin family has been reported, and the mechanism of action of this toxin remains unclear. Here, we report the first structure of this toxin family, revealing a structural fold composed of 5 + 3-helix bundles. Further analysis by protein truncation and site-directed mutagenesis indicated that the N-terminal 5-helix bundle is responsible for membrane permeabilization, whereas the C-terminal 3-helix bundle is likely responsible for host receptor binding. Interestingly, the C-terminal domain inhibited the activity of both full-length toxin and its N-terminal domain. Moreover, we observed that the linker region is highly conserved and has a conserved DL XXX D X AT sequence motif. Structurally, this linker region extensively interacted with both terminal CAMP factor domains, and mutagenesis disclosed that the conserved sequence motif is required for CAMP factor's co-hemolytic activity. In conclusion, our results reveal a unique structure of this bacterial toxin and help clarify the molecular mechanism of its co-hemolytic activity.
Organizational Affiliation:
From the Hefei National Laboratory for Physical Sciences at Microscale, CAS Key Laboratory of Innate Immunity and Chronic Disease, School of Life Sciences and Medical Center, University of Science and Technology of China, Hefei, Anhui 230027, China, jint@ustc.edu.cn.
