Role of the Bloom syndrome DNA helicase BLM in chromosome maintenance mechanisms

布卢姆综合征 DNA 解旋酶 BLM 在染色体维持机制中的作用

• 批准号: 9125836
• 负责人: Kristina Schmidt
• 金额: $ 29.27万
• 依托单位: UNIVERSITY OF SOUTH FLORIDA
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-01 至 2019-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9125836
• 关键词: ATP Hydrolysis; ATP phosphohydrolase; Adopted; Affect; African; Aging; Alleles; Amino Acids; BLM gene; Bacteria; Binding; Binding Proteins; Biochemical; Bloom Syndrome; C-terminal; Cancer Etiology; Cells; Chimera organism; Chromosomal Instability; Chromosomal Rearrangement; Chromosomal Stability; Chromosome Breakage; Chromosomes; Cleaved cell; Code; Cruciform DNA; DNA; DNA Binding; DNA Damage; DNA Repair; Defect; Delayed Hypersensitivity; Development; Disease; Double Strand Break Repair; Elements; Employee Strikes; Evaluation; Event; Exons; Experimental Designs; Frequencies; Functional disorder; General Population; Genes; Genetic; Genetic Recombination; Genome; Genome Stability; Genomic Instability; Goals; Health; High-Risk Cancer; Human; Hydrolysis; Hypersensitivity; Incidence; Introns; Lead; Libraries; Life; Light; Link; Maintenance; Malignant Neoplasms; Maps; Metabolic; Missense Mutation; Molecular; Mutagenesis; Mutation; N-terminal; NMR Spectroscopy; Non-Insulin-Dependent Diabetes Mellitus; Nuclear Magnetic Resonance; Persons; Phenotype; Population; Predisposition; Proline; Protein Region; Proteins; Refractory; Reporting; Risk Factors; Role; Sequence Analysis; Single Nucleotide Polymorphism; Sister Chromatid Exchange; Structure; Symptoms; Syndrome; Tail; Testing; Variant; Werner Syndrome; Yeasts; alpha helix; associated symptom; base; cancer risk; design; genome integrity; helicase; homologous recombination; in vivo; insight; loss of function; molecular recognition; mutant; novel; population based; repaired; response

 DESCRIPTION (provided by applicant): Defects in many genes with roles in DNA break repair are associated with a striking predisposition to cancer development. One of the most extreme cancer risks is associated with Bloom syndrome (BS) - a chromosome breakage disorder caused by mutations in the RecQ-like DNA helicase BLM. RecQ-like helicases and their role in regulating recombinational DNA repair are conserved from bacteria to humans. Besides BS, defects in RecQ-related genes cause Werner syndrome and Rothmund-Thompson syndrome, which are characterized by accelerated aging and/or increased cancer risk. In addition to BS-associated mutations, 93 missense mutations in the human BLM gene have been reported, but it is unknown which, if any, affect BLM function. It has also been suggested that single nucleotide polymorphisms (SNPs) in introns of BLM that have been associated with higher cancer risk may be linked to coding SNPs in exons of BLM. Using a yeast Sgs1-BLM chimera, we have identified coding SNPs that impair BLM function. They include hypomorphic mutations that define a new class of BLM alleles, not associated with BS, that may increase genome instability, cancer risk and other BS-associated symptoms. One objective of this proposal therefore is to determine the effect of coding SNPs throughout the BLM gene on chromosome stability, DNA break repair and the DNA-damage response, and identify their biochemical defects. In contrast to the helicase core, the >600-residue long N- terminal tails of BLM and the related yeast helicase Sgs1 are disordered and not conserved at the sequence level. They have therefore been refractory to conventional approaches to elucidate their function. It is our hypothesis that the function of the long tails of Sgs1 and BLM arises from structural elements, embedded in disorder, that serve as molecular recognition elements for binding proteins. To test this hypothesis we have designed an approach that combines computational prediction of disorder and interactivity, structure analysis by nuclear magnetic resonance (NMR) spectroscopy, and proline mutagenesis to identify these structural elements and elucidate their importance for BLM and Sgs1 function. Specifically we will (1) use a population- based mutational approach to identify and characterize novel functional motifs in BLM; the ability of BLM variants to rescue high sister-chromatid exchange, double-strand-break-repair defects and hypersensitivity to DNA-damaging agents will be assessed; (2) identify biochemical defects of functionally impaired BLM variants by assessing ATPase, DNA binding, annealing and unwinding activities, and (3) determine disorder-function relationships in the N-terminal tails of Sgs1 and BLM using a combination of (a) NMR to identify regions that are dynamically constrained and may adopt interaction-prone a-helices, (b) proline mutagenesis to disrupt the structural motifs, and (c) functional analysis of novel separation-of-function alleles of SGS1 and BLM in vivo. New insights into function and connectivity of BLM and Sgs1 will elucidate the mechanisms of hyper- recombination and chromosome instability in Bloom syndrome and, generally, in human cancers.

 描述（由适用提供）：许多在DNA断裂修复中作用的基因缺陷与癌症发展的打击倾向有关。最极端的癌症风险之一是与Bloom综合征（BS）有关，这是由RECQ样DNA旋转酶BLM突变引起的染色体破裂障碍。从细菌到人类，RECQ样解旋酶及其在调节重组DNA修复中的作用是保守的。除BS外，与RECQ相关基因的缺陷导致Werner综合征和Rothmund-Thompson综合征，其特征在于加速衰老和/或增加癌症风险。除了与BS相关的突变外，还报道了人类BLM基因中的93个错义突变，但尚不清楚哪个（如果有的话）会影响BLM功能。还有人提出，与较高的癌症风险有关的BLM内含子中的单个核苷酸多态性（SNP）可能与BLM外显子中的SNP有关。使用酵母SGS1-BLM嵌合体，我们确定了损害BLM功能的编码SNP。其中包括定义新类别的BLM等位基因（与BS无关的新类别）的型型突变，这些突变可能会增加基因组不稳定性，癌症风险和其他BS相关符号。因此，该提案的一个目的是确定整个BLM基因对染色体稳定性，DNA断裂修复和DNA破坏反应的编码影响，并确定其生化缺陷。与解旋酶核心相反，BLM和相关酵母解旋酶SGS1的> 600个残留长的N端尾是无序的，并且不在序列水平上配置。因此，它们对阐明其功能的常规方法是难治性的。我们的假设是，SGS1和BLM的长尾巴的功能来自嵌入无序的结构元素，它们是结合蛋白的分子识别元素。为了检验这一假设，我们设计了一种方法，该方法结合了混乱和互动性的计算预测，核磁共振（NMR）光谱的结构分析以及脯氨酸诱变，以识别这些结构元素，并阐明其对BLM和SGS1功能的重要性。具体而言，（1）使用基于人群的突变方法来识别和表征BLM中新型功能基序；将评估BLM变体挽救高级姐妹染色剂交换，双链破裂的缺陷以及对DNA损害剂的超敏反应的能力； (2) identify biochemical defects of functionally impaired BLM variants by assessing ATPase, DNA binding, annealing and unwinding activities, and (3) determine disorder-function relationships in the N-terminal tails of Sgs1 and BLM using a combination of (a) NMR to identify regions that are dynamically constrained and may adopt interaction-prone a-helices, (b) proline mutagenesis to disrupt the structural基序，（c）体内SGS1和BLM的新型功能分离等位基因的功能分析。对BLM和SGS1功能和连通性的新见解将阐明Bloom综合征中的超混合和染色体不稳定性的机制，并且通常在人类癌症中。