The Gram-negative bacterium Yersinia pestis, the causative agent of the plague, is extremely virulent. Upon infection, Y. pestis injects a set of effector proteins into macrophages that suppresses their phagocytic behavior and also interferes with their innate immune responses. One of the effector proteins, YopJ, acetylates serines and threonines on various MAP kinases, including the MAP kinase kinase kinase TAK1, which controls a key signaling step in the innate immune response pathway. To determine how YopJ interferes with TAK1, you transfect human cells with active YopJ (YopJ^WT) or inactive YopJ (YopJ^CA) and with FLAG-tagged active TAK1 (TAK1WT) or inactive TAK1 (TAK1^K63W), and assay for total TAK1 and for phosphorylated TAK1, using antibodies against the FLAG tag or against phosphorylated TAK1 (Figure Q23–1). How does YopJ block the TAK1 signaling pathway? How do you suppose the serine/threonine acetylase activity of YopJ might interfere with TAK1 activation?

Figure Q23-1

Transcribed Image Text:

TAK1 WT ТАК1 WT WT K63W YopJ CA WT kd IP: a-FLAG-TAK1 IB: a-PTAK1 -76 IP: a-FLAG-TAK1 -76 IB: a-FLAG-TAK1 1 2 3 4