TTC33 forms a complex with WDR61 and PHF5A to recruit factors relevant to genomic integrity

The functions of many human proteins remain unknown, highlighting major gaps in our understanding of cellular biology. TTC33 is an evolutionarily conserved tetratricopeptide repeat (TPR) protein expressed across human tissues, whose molecular role is not defined. Here we identify the TTC33 partners using comparative label-free mass spectrometry. The TTC33-associated network (TAN) comprises WDR61, CCDC97, UNG1/2, PP2A-B55α, PHF5A, and components of the SF3B U2 spliceosomal complex. Using a combination of biochemical assays, structural modeling and molecular dynamics we show that TTC33 directly recruits WDR61 and PHF5A to assemble into a trimeric core complex (TANC), which then forms distinct interactions with either UNG1/2 or SF3B-CCDC97. Somatic TTC33 mutations at key TANC interface residues reduce complex stability and weaken the interaction network. We further show that WDR61 stabilizes TTC33 by protecting it from proteolytic degradation. Loss of network components induces genomic instability and activates DNA damage markers, including γH2AX and p53 phosphorylation.