Yersinia
bacteria target Yop effector toxins to the interior of host immune cells by the
Ysc-Yop type III secretion system. A YopN-TyeA heterodimer is central to controlling
Ysc-Yop targeting activity. A
+
1 frameshift event in the 3-prime end of
yopN
can also
produce a singular secreted YopN-TyeA polypeptide that retains some regulatory function
even though the C-terminal coding sequence of this YopN differs greatly from wild type.
Thus, this YopN C-terminal segment was analyzed for its role in type III secretion control.
Bacteria producing YopN truncated after residue 278, or with altered sequence between
residues 279 and 287, had lost type III secretion control and function. In contrast,
YopN variants with manipulated sequence beyond residue 287 maintained full control
and function. Scrutiny of the YopN-TyeA complex structure revealed that residue W
279
functioned as a likely hydrophobic contact site with TyeA. Indeed, a YopN
W
279
G
mutant
lost all ability to bind TyeA. The TyeA residue F
8
was also critical for reciprocal YopN
binding. Thus, we conclude that specific hydrophobic contacts between opposing YopN
and TyeA termini establishes a complex needed for regulating Ysc-Yop activity.