Team:Korea U Seoul/Team/Attributions/content

Background

Sortases, enzymes that recognize and cleave the specific sorting signal of secreted proteins to form isopeptide bonds between the secreted proteins and polypeptides, function as protein ligase to form the cell-wall surface of gram-positive bacteria. In case of C.diphtheriae, which belongs to the same genus of our experimental bacteria Corynebacterium glutamicum, has total of 6 sortases, 5 pilus specific sortases (Srt A,B,C,D,E) and 1 housekeeping sortase (Srt F) involved in the formation of all types of pili.
There are 9 types of pillins that comprise pilus; Spa A, B, C, D, E, F, G, H, I, J. SrtA build up SpaA-type pili, which is composed of Spa A, B and C. Srt B/C and Srt d/E each forms SpaD-type pili and SpaH-type pili, which is made up of Spa D, E, F and Spa H, I, J respectively. Like this, the names of each pili types are generally from the names of many Spa proteins.
The picture below shows the process of SpaA type pili formation, using SrtA. Sortase class A enzymes recognize the sequence LPXTG at the carboxyl terminus of surface protein precursors. Cystein of SrtA recognizes LPXTG motif of SpaC, cleaves between T and G, forming SpaC-SrtA intermediate via nucleophilic attack. This intermediate is again attacked by lysine of SrtA bounded SpaA, and the process is continued to form SpaC–SpaAn–SrtA intermediates.
Nucleophilic attack by Lysine of SrtF bounded SpaB form SpaC-SpaA(n)-SpaB-SrtF intermediate. The product of this SrtA reaction is covalently linked to lipidⅡ and is then incorporated into the cell wall envelope, terminating the formation of SpaA-type pilus.