Plasmodium falciparum SSB Tetramer Wraps Single-Stranded DNA with Similar Topology but Opposite Polarity to E. coli SSB

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• 作者：Edwin Antony¹ ; Elizabeth A. Weiland¹ ; Sergey Korolev² ; ^{korolevs@slu.edu} ; Timothy M. Lohman¹ ; ^{lohman@biochem.wustl.edu}
• 关键词：TCEP ; tris(2-carboxyethyl)phosphine ; 2-ME ; 2-mercaptoethanol ; ALS ; apicoplast localization signal ; SSB ; single-stranded DNA binding ; ssDNA ; single-stranded DNA ; Pf-SSB ; P. falciparum SSB ; Ec-SSB ; Escherichia coli SSB ; PDB ; Protein Data Bank ; EDTA ; ethylen
• 刊名：Journal of Molecular Biology
• 出版年：2012
• 期刊代码：102_00222836
• 类别：imm
• 出版时间：20 July, 2012
• 卷：420
• 期：4-5
• 页码：269-283
• 文件大小：2006 K

摘要

Single-stranded DNA binding (SSB) proteins play central roles in genome maintenance in all organisms. <em>Plasmodium falciparumem>, the causative agent of malaria, encodes an SSB protein that localizes to the apicoplast and likely functions in the replication and maintenance of its genome. <em>P. falciparumem> SSB (<em>Pfem>-SSB) shares a high degree of sequence homology with bacterial SSB proteins but differs in the composition of its C-terminus, which interacts with more than a dozen other proteins in <em>Escherichia coliem> SSB (<em>Ecem>-SSB). Using sedimentation methods, we show that <em>Pfem>-SSB forms a stable homo-tetramer alone and when bound to single-stranded DNA (ssDNA). We also present a crystal structure at 2.1聽脜 resolution of the <em>Pfem>-SSB tetramer bound to two (dT)₃₅ molecules. The <em>Pfem>-SSB tetramer is structurally similar to the <em>Ecem>-SSB tetramer, and ssDNA wraps completely around the tetramer with a 鈥渂aseball seam鈥?topology that is similar to <em>Ecem>-SSB in its 鈥?5 binding mode鈥? However, the polarity of the ssDNA wrapping around <em>Pfem>-SSB is opposite to that observed for <em>Ecem>-SSB. The interactions between the bases in the DNA and the amino acid side chains also differ from those observed in the <em>Ecem>-SSB-DNA structure, suggesting that other differences may exist in the DNA binding properties of these structurally similar proteins.