Identification of Set11 from Staphylococcus aureus Mu50 strain as a ortholog of SSL7 via bioinformatic analysis and determination of its possible targets from human serum using CNBr-pull down assays
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To identify and characterize staphylococcus exotoxin-like (SET) protein Set11 from Staphylococcus aureus Mu50 strain and its possible targets proteins from human blood/serum.
Set11 is a member of the staphylococcal superantigen-like (SSL) proteins (also called Staphylococcus exotoxin-like (SET) proteins) family that is found in staphylococcal strain Mu50. Its structure and function, however, remain unknown. We performed bioinformatics analysis of Set11: it had 90% sequence identity to SSL7 in NCTC 8325 strain, indicating Set11 is a SSL7 ortholog. SSL7 in ATCC 12598 strain binds complement C5 to inhibit complement system. To investigate if Set11 binds C5, we made the homology model of Set11 and the Set11-C5 complex model based on SSL7 and SSL7-C5 structures, respectively. Structural analysis and sequence alignment reveal that the residues in SSL7 involved in C5 binding are conserved in Set11, indicating C5 as the potential target for Set11. To identify new targets of Set11, we cloned, expressed and purified Set11 and performed CNBr-pull down combined mass spectrum assays using human blood and serum.
We identified Set11 as the ortholog of SSL7 and determined C5, fibronectin 1 isoform 3 preproprotein, albumin, alpha-1-microglobulin precursor and complement C3 processor as the potential target proteins for Set11, indicating new functions of Set11/SSL7.
KeywordsAlbumin Bioinformatics Exotoxin-like protein C5 Set11 Staphylococcus aureus Structure model SSL7
This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB 08010101), the National Key Research and Development Program of China (Nos. 2016YFA0400903) and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Nos. 31621002). This work was also supported by the National Natural Science Foundation of China (Nos. U1532109, 31370756, and 31361163002), and the Scientific Research Grant of Hefei Science Center of CAS (Nos. 2015SRG-HSC043, 2015HSC-UP019) to JZ. This work was also supported by the Anhui Provincial Natural Science Foundation (Nos. 1608085QC52) to XZ and the National Natural Science Foundation of China (Nos. 31400627) to MW.
Supplementary Table 1—Sequences of Set11 and SSL proteins.
Supplementary Table 2—LC-MS/MS results for possible targets of Set11 from human blood/serum.
Supplementary Fig. 1—Structural comparison of Set11 model and SSL7 (PDB ID: 1V1O).
Supplementary Fig. 2—Structure model of Set11-C5.
Supplementary Fig. 3—Signal-peptide prediction of Set11.
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Conflict of interest
The authors declare that they have no conflict of interest.
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