7rcb
Crystal Structure of a PMS2 VUS
Structural highlights
DiseasePMS2_HUMAN Defects in PMS2 are the cause of hereditary non-polyposis colorectal cancer type 4 (HNPCC4) [MIM:614337. Mutations in more than one gene locus can be involved alone or in combination in the production of the HNPCC phenotype (also called Lynch syndrome). Most families with clinically recognized HNPCC have mutations in either MLH1 or MSH2 genes. HNPCC is an autosomal, dominantly inherited disease associated with marked increase in cancer susceptibility. It is characterized by a familial predisposition to early onset colorectal carcinoma (CRC) and extra-colonic cancers of the gastrointestinal, urological and female reproductive tracts. HNPCC is reported to be the most common form of inherited colorectal cancer in the Western world, and accounts for 15% of all colon cancers. Cancers in HNPCC originate within benign neoplastic polyps termed adenomas. Clinically, HNPCC is often divided into two subgroups. Type I: hereditary predisposition to colorectal cancer, a young age of onset, and carcinoma observed in the proximal colon. Type II: patients have an increased risk for cancers in certain tissues such as the uterus, ovary, breast, stomach, small intestine, skin, and larynx in addition to the colon. Diagnosis of classical HNPCC is based on the Amsterdam criteria: 3 or more relatives affected by colorectal cancer, one a first degree relative of the other two; 2 or more generation affected; 1 or more colorectal cancers presenting before 50 years of age; exclusion of hereditary polyposis syndromes. The term 'suspected HNPCC' or 'incomplete HNPCC' can be used to describe families who do not or only partially fulfill the Amsterdam criteria, but in whom a genetic basis for colon cancer is strongly suspected.[1] [2] Defects in PMS2 are a cause of mismatch repair cancer syndrome (MMRCS) [MIM:276300; also known as Turcot syndrome or brain tumor-polyposis syndrome 1 (BTPS1). MMRCS is an autosomal dominant disorder characterized by malignant tumors of the brain associated with multiple colorectal adenomas. Skin features include sebaceous cysts, hyperpigmented and cafe au lait spots.[3] [4] [5] [6] FunctionPMS2_HUMAN Component of the post-replicative DNA mismatch repair system (MMR). Heterodimerizes with MLH1 to form MutL alpha. DNA repair is initiated by MutS alpha (MSH2-MSH6) or MutS beta (MSH2-MSH6) binding to a dsDNA mismatch, then MutL alpha is recruited to the heteroduplex. Assembly of the MutL-MutS-heteroduplex ternary complex in presence of RFC and PCNA is sufficient to activate endonuclease activity of PMS2. It introduces single-strand breaks near the mismatch and thus generates new entry points for the exonuclease EXO1 to degrade the strand containing the mismatch. DNA methylation would prevent cleavage and therefore assure that only the newly mutated DNA strand is going to be corrected. MulL alpha (MLH1-PMS2) interacts physically with the clamp loader subunits of DNA polymerase III, suggesting that it may play a role to recruit the DNA polymerase III to the site of the MMR. Also implicated in DNA damage signaling, a process which induces cell cycle arrest and can lead to apoptosis in case of major DNA damages.[7] [8] Publication Abstract from PubMedHereditary cancer syndromes account for approximately 5%-10% of all diagnosed cancer cases. Lynch syndrome (LS) is an autosomal dominant hereditary cancer condition that predisposes individuals to an elevated lifetime risk for developing colorectal, endometrial, and other cancers. LS results from a pathogenic mutation in one of four mismatch repair (MMR) genes (MSH2, MSH6, MLH1, and PMS2). The diagnosis of LS is often challenged by the identification of missense mutations, termed variants of uncertain significance, whose functional effect on the protein is not known. Of the eight PMS2 variants initially selected for this study, we identified a variant within the N-terminal domain where asparagine 335 is mutated to serine, p.Asn335Ser, which lacked ATPase activity, yet appears to be proficient in MMR. To expand our understanding of this functional dichotomy, we performed biophysical and structural studies, and noted that p.Asn335Ser binds to ATP but is unable to hydrolyze it to ADP. To examine the impact of p.Asn335Ser on MMR, we developed a novel in-cell fluorescent-based microsatellite instability reporter that revealed p.Asn335Ser maintained genomic stability. We conclude that in the absence of gross structural changes, PMS2 ATP hydrolysis is not necessary for proficient MMR and that the ATPase deficient p.Asn335Ser variant is likely benign. PMS2 variant results in loss of ATPase activity without compromising mismatch repair.,D'Arcy BM, Arrington J, Weisman J, McClellan SB, Vandana, Yang Z, Deivanayagam C, Blount J, Prakash A Mol Genet Genomic Med. 2022 Feb 21:e1908. doi: 10.1002/mgg3.1908. PMID:35189042[9] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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