Crystal Structure of a Single-Stranded DNA-Binding Protein (TM0604) from Thermotoga maritima at 2.60 A Resolution

摘要

Introduction. The TM0604 gene of Thermotoga maritima encodes a single-stranded DNA-binding protein (SSB) with a molecular weight of 16,166 Da (residues 1-141) and a calculated isoelectric point of 4.8. SSB plays essential roles hi DNA replication, recombination, and repair. SSB, also known as helix-destabilizing protein, binds tightly to single-stranded DNA (ssDNA) as a homotet-ramer. SSB from E. coli can bind long ssDNAs in two main binding modes, which occlude 35 or 65 nucleotides per tetramer, depending on how many SSB subunits from the tetramer interact with ssDNA. In the SSB_?35? binding mode, two SSB subunits per tetramer interact with ssDNA and self-assemble into long clusters. In the SSB_?65? binding mode, all four SSB subunits interact with ssDNA and do not form clusters. Closely related variants of SSB are encoded in the genome of a variety of large, self-transmissible plasmids. The eukaryotic mitochondrial proteins that bind ssDNA are structurally and evolutionarily related to prokaryotic SSB and are probably involved in mitochondrial DNA replication. Here, we report the crystal structure of TM0604, which was determined using the semiau-tomated, high-throughput pipeline of the Joint Center for Structural Genomics (JCSG).