Forkhead-associated (FHA) domains are small phosphopeptide recognition modules mostly found in eubacteria and eukaryotes. It is about 95-120 residues long that fold into an 11-stranded beta-sandwich. FHA domains can mediate the recognition of phosphorylated and non-phosphorylated substrates, as well as protein oligomerization. They specifically recognize threonine phosphorylation (pThr) accompanying activation of protein serine/threonine kinases. FHA domains show diverse ligand specificity. They may recognize the pTXXD motif, the pTXXI/L motif, and TQ clusters (singly and multiply phosphorylated). In eukaryotes, FHA superfamily members include forkhead-type transcription factors, as well as other signaling proteins, such as many regulatory proteins, kinases, phosphatases, motor proteins called kinesins, and metabolic enzymes. Many of them localize to the nucleus, where they participate in establishing or maintaining cell cycle checkpoints, DNA repair, or transcriptional regulation. FHA domains play important roles in human diseases, particularly in relation to DNA damage responses and cancers. In bacteria, FHA domain-containing proteins may participate in injection of viral proteins into host cells, transmembrane transporters, and cell division. FHA domain-containing proteins rarely include more than one copy of the domain. The only exception in eukaryotes is the checkpoint kinase Rad53 from Saccharomyces cerevisiae, which harbors two FHA domains (FHA1 and FHA2) flanking a central kinase domain. The two FHA domains recognize different phosphorylated targets and function independently from one another. In contrast, Mycobacterium tuberculosis ABC transporter Rv1747 contains two FHA domains but only one of them is essential for protein function.
Feature 1:phosphopeptide binding site [polypeptide binding site]
Evidence:
Comment:GR at the C terminus of strand beta3, SRxH just preceding beta5, and motif SxNG in the beta6-beta7 turn indicate a canonical mode of pThr recognition.
Structure:2PIE; Homo sapiens RNF8 in complex with its optimal phosphopeptide, contacts at 4A
Comment:Conserved residues are involved in binding directly to the ligand backbone and phosphate group. Non-conserved residues may determine binding specificity.
Comment:some members lack the conserved residues that are required for binding phosphothreonine
Jiyao W et al.(2023). "The conserved domain database in 2023.",