Albany 2015:Book of Abstracts
June 9-13 2015
©Adenine Press (2012)
Structurally Distinct Ubiquitin- and SUMO-Modified PCNA: Implications for their Distinct Roles in the DNA Damage Response
Proliferating cell nuclear antigen (PCNA) is a pivotal replication protein, which also controls cellular responses to DNA damage. PCNA binds core replisomal constituents, numerous repair and cell cycle control proteins, acting as a platform for the assembly of the replication machinery. Posttranslational modifications of PCNA by ubiquitin (Ub) and SUMO play a critical role in coordinating DNA damage responses to suppress genome instability (Ulrich et al., 2010, 2012; Armstrong et al., 2012). How the modifiers alter PCNA-dependent DNA repair and damage tolerance pathways has so far remained elusive. We used integrative modeling methods (Tsutakawa et al., 2011) to identify atomic models of PCNAK107-Ub, PCNAK164-Ub and PCNAK164-SUMO complexes consistent with solution small angle X-ray scattering (SAXS) data. We show that Ub and SUMO have distinct modes of association to PCNA. Ubiquitin adopts discrete docked binding conformations and the position of ubiquitin attachment, 107 versus 164, alters conformation. By contrast, SUMO associates by simple tethering and adopts extended flexible conformations. These structural differences are the result of the opposite electrostatic potentials of SUMO and Ub. The unexpected contrast in conformational behavior of Ub-PCNA and SUMO-PCNA has implications for interactions with partner proteins, interacting surfaces accessibility, and access points for pathway regulation.
This research was supported by NSF CAREER Award MCB-1149521.
H. D. Ulrich (2012) Ubiquitin and SUMO in DNA repair at a glance. J Cell Sci, 125, 249-254.
A. A. Armstrong, F. Mohideen, & C. D. Lima (2012) Recognition of SUMO-modified PCNA requires tandem receptor motifs in Srs2. Nature, 483, 59-63.
S. E. Tsutakawa, A.W. Van Wynsberghe, B. D. Freudenthal, C. P. Weinacht, L. Gakhar, M. T. Washington, Z. Zhuang, J. A. Tainer, & Ivanov, I. (2011). Solution X-ray scattering combined with computational modeling reveals multiple conformations of covalently bound ubiquitin on PCNA. Proc Natl Acad Sci USA 108, 17672-17677.
Susan E. Tsutakawa1
1Lawrence Berkeley National Laboratory