Structure-specific recognition protein-1 (SSRP1) is an elongated homodimer that binds histones

• DOI: 10.1074/jbc.ra117.000994
• Publication Date: 2018-05-15T20:07:27Z
• Authors: Gabriele Marcianò; Stefano Da Vela; Giancarlo Tria; Dmitri I. Svergun; Olwyn Byron; Danny T. Huang
• Keywords: CHROMATIN; 0301 basic medicine; homodimer; small-angle X-ray scattering (SAXS); Protozoan Proteins; 610; histone; SSRP1; oligomerization; SACCHAROMYCES-CEREVISIAE; Histones; 03 medical and health sciences; Protein Domains; CHAPERONE FACT; DNA-POLYMERASE ALPHA; Humans; H3-H4; Dictyostelium; Amino Acid Sequence; Protein Structure, Quaternary; info:eu-repo/classification/ddc/610; NUCLEOSOME REORGANIZATION; N-TERMINAL DOMAIN; High Mobility Group Proteins; SMALL-ANGLE SCATTERING; DNA-Binding Proteins; histone chaperone; REPLICATION; SPT16; Protein Structure and Folding; H2A-H2B; Protein Multimerization; Transcriptional Elongation Factors; TRANSCRIPTIONAL ACTIVATION; analytical ultracentrifugation; Protein Binding

JBC papers in press 293(26), 10071 - 10083 (2018). doi:10.1074/jbc.RA117.000994<br/>Published by ASBMB, Bethesda, MD.<br/>The histone chaperone complex facilitates chromatin transcription (FACT) plays important roles in DNA repair, replication, and transcription. In the formation of this complex, structure-specific recognition protein-1 (SSRP1) heterodimerizes with suppressor of Ty 16 (SPT16). SSRP1 also has SPT16-independent functions, but how SSRP1 functions alone remains elusive. Here, using analytical ultracentrifugation (AUC) and small-angle X-ray scattering (SAXS) techniques, we characterized human SSRP1 and that from the amoeba Dictyostelium discoideum and show that both orthologs form an elongated homodimer in solution. We found that substitutions in the SSRP1 pleckstrin homology domain known to bind SPT16 also disrupt SSRP1 homodimerization. Moreover, AUC and SAXS analyses revealed that SSRP1 homodimerization and heterodimerization with SPT16 (resulting in FACT) involve the same SSRP1 surface, namely the PH2 region, and that the FACT complex contains only one molecule of SSRP1. These observations suggest that SSRP1 homo- and heterodimerization might be mutually exclusive. Moreover, isothermal titration calorimetry analyses disclosed that SSRP1 binds both histones H2A–H2B and H3–H4 and that disruption of SSRP1 homodimerization decreases its histone-binding affinity. Together, our results provide evidence for regulation of SSRP1 by homodimerization and suggest a potential role for homodimerization in facilitating SPT16-independent functions of SSRP1.<br/>