Baker Chrissy N S, Pajela Precious Grace C, Martin Davis E, Dzyuba Sergei V, Stewart Mikaela D
Department of Biology, Texas Christian University, Fort Worth, Texas, USA.
Department of Chemistry and Biochemistry, Texas Christian University, Fort Worth, Texas, USA.
Protein Sci. 2025 Jan;34(1):e5240. doi: 10.1002/pro.5240.
Inherited mutations in the genes coding for the tumor suppressor proteins BRCA1 and PALB2 can lead to increased risk of breast and ovarian cancer. Upon DNA damage, these two proteins form a complex to promote double-stranded break repair via homologous recombination. Missense mutations in either BRCA1 or PALB2 that disrupt this important interaction result in loss of effective DNA damage repair and are associated with breast tumorigenesis. However, the overwhelming majority of missense mutations found in the binding domains of these two genes remain classified as variants of unknown significance. Here we report an in vitro assay for assessing the effect of variants of unknown significance on the heterodimerization of PALB2 and BRCA1 that recapitulates the effect of the known deleterious mutations. We apply the assay to several variants of unknown significance in BRCA1 which reveals other mutations in this region that also disrupt binding, including a mutation of a residue not predicted to directly interact with PALB2. Structural analysis indicates that all BRCA1 mutations to proline tested disrupt α-helix formation and therefore are not well tolerated even when located at positions outside of the PALB2-binding interface. This assay and the structural hypothesis described will be helpful for assessing risk for variants identified in the future in the BRCA1/PALB2 interaction domains.
编码肿瘤抑制蛋白BRCA1和PALB2的基因发生遗传突变会导致乳腺癌和卵巢癌风险增加。在DNA受损时，这两种蛋白会形成复合物，通过同源重组促进双链断裂修复。BRCA1或PALB2中破坏这种重要相互作用的错义突变会导致有效的DNA损伤修复功能丧失，并与乳腺肿瘤发生相关。然而，在这两个基因的结合域中发现的绝大多数错义突变仍被归类为意义未明的变异。在此，我们报告一种体外检测方法，用于评估意义未明的变异对PALB2和BRCA1异源二聚化的影响，该方法概括了已知有害突变的作用。我们将该检测方法应用于BRCA1中几个意义未明的变异，发现该区域的其他突变也会破坏结合，包括一个预测不会直接与PALB2相互作用的残基的突变。结构分析表明，所有测试的BRCA1脯氨酸突变都会破坏α螺旋形成，因此即使位于PALB2结合界面之外的位置也不能很好地耐受。这种检测方法和所描述的结构假说将有助于评估未来在BRCA1/PALB2相互作用域中鉴定出的变异的风险。
