Structural insights into multifunctionality of human FACT complex subunit hSSRP1.

Human structure-specific recognition protein 1 (hSSRP1) is an essential component of the facilitates chromatin transcription complex, which participates in nucleosome disassembly and reassembly during gene transcription and DNA replication and repair. Many functions, including nuclear localization, histone chaperone activity, DNA binding, and interaction with cellular proteins, are attributed to hSSRP1, which contains multiple well-defined domains, including four pleckstrin homology (PH) domains and a high-mobility group domain with two flanking disordered regions. However, little is known about the mechanisms by which these domains cooperate to carry out hSSRP1's functions. Here, we report the biochemical characterization and structure of each functional domain of hSSRP1, including the N-terminal PH1, PH2, PH3/4 tandem PH, and DNA-binding high-mobility group domains. Furthermore, two casein kinase II binding sites in hSSRP1 were identified in the PH3/4 domain and in a disordered region (Gly617-Glu709) located in the C-terminus of hSSRP1. In addition, a histone H2A-H2B binding motif and a nuclear localization signal (Lys677‒Asp687) of hSSRP1 are reported for the first time. Taken together, these studies provide novel insights into the structural basis for hSSRP1 functionality.