Poster abstracts
Poster number 8 submitted by Brian Caldwell
Crystal Structure of a Minimal Synaptosome Complex for DNA Repair by Single Strand Annealing
Brian J. Caldwell (OSBP), Chris E. Smith (OSBP), Charles E. Bell (Biological Chemistry and Pharmacology )
Abstract:
Single strand annealing (SSA) is one of three main pathways for repair of double stranded DNA breaks, a deleterious form of DNA damage that can lead to chromosome rearrangement. Bacteriophage lambda uses a simple two component “SynExo” (Synaptase-Exonuclease) recombination system for SSA that consists of a 5’-3’ exonuclease to resect DNA ends, and a protein called Red beta to anneal the resulting 3’ overhang to a complementary strand. Similar recombination systems exist in a wide variety of bacteriophage as well as in oncogenic dsDNA viruses such as HSV1. Due to the highly-evolved and simple nature of this recombination system, a mechanistic understanding of how it operates would provide a useful model for studying the more elaborate SSA reaction in mammalian cells. In addition, the SynExo proteins from bacteriophage lambda have been exploited in powerful new methods for genome engineering. Interestingly, the two components of the SynExo system in bacteriophage lambda form a complex called a “synaptosome”. The exact role of this complex is unknown but it may serve to integrate the two steps of the SSA reaction by physically loading the annealing protein onto the 3’ overhang as it is generated by the exonuclease. Knowledge of the overall architecture of the complex will shed light on how it operates. Here we have used x-ray crystallography to solve the structure of a “mini” synaptosome complex containing a lambda exonuclease trimer bound to three copies of the Red Beta C-terminal domain. The structure reveals the residues of each protein at the interface and thus provides a framework for design of mutational experiments to probe the role of the complex in promoting recombination in vivo.
Keywords: SynExo, Synaptosome