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Pseudokinase domain of Tribbles Homolog proteins The pseudokinase domain shows similarity to protein kinases but lacks crucial residues for catalytic activity. Tribbles Homolog (TRB) proteins interact with many proteins involved in signaling pathways. They play scaffold-like regulatory functions and affect many cellular processes such as mitosis, apoptosis, differentiation, and gene expression. TRB proteins bind to the middle kinase in mitogen activated protein kinase (MAPK) signaling cascades, MAPK kinases. They regulate the activity of MAPK kinases, and thus, affect MAPK signaling. In Drosophila, Tribbles regulates String, the ortholog of mammalian Cdc25, during morphogenesis. String is implicated in the progression of mitosis during embryonic development. Vertebrates contain three TRB proteins encoded by three separate genes: Tribbles-1 (TRB1 or TRIB1), Tribbles-2 (TRB2 or TRIB2), and Tribbles-3 (TRB3 or TRIB3). The TRB subfamily is part of a larger superfamily that includes the catalytic domains of serine/threonine kinases, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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