The nuclear factor kappa B (NFκB) family is a group of homo and heterodimeric transcription factors regulating over 600 genes. These genes are responsible for a variety of key cellular functions including T cell activation, apoptosis, and immune response. NFκB requires RPS3 (ribosomal protein S3) as a co-activator for approximately 50% of its transcription activatable genes. Certain pathways such as hepatocellular carcinoma, lymphoblastic leukemia, and oral squamous cell carcinoma are dependent on the presence of both proteins. We determined that while there was no direct interaction between RPS3 and NFκB, both proteins can bind to IκBα (inhibitor of κB-alpha) and form a ternary complex. Hydrogen-deuterium exchange mass spectrometry (HDX-MS) reveals that RPS3 is very disordered in the apo state and folds upon binding to IκBα. Although the HDX-MS of NFκB is the same in the binary IκBα-NFκB and ternary IκBα-RPS3-NFκB complex, RPS3 adopts different conformations in the IκBα-RPS3 and ternary IκBα-NFκB-RPS3 complexes. We are pursuing structures of the binary and ternary complexes by cryo-electron microscopy to reveal how RPS3 and IκBα interact with NFκB.
Cai et al. (Sun,) studied this question.