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A Lynch syndrome-associated mutation at a Bergerat ATP-binding fold destabilizes the structure of the DNA mismatch repair endonuclease MutL.

ABSTRACT: In humans, mutations in genes encoding homologs of the DNA mismatch repair endonuclease MutL cause a hereditary cancer that is known as Lynch syndrome. Here, we determined the crystal structures of the N-terminal domain (NTD) of MutL from the thermophilic eubacterium Aquifex aeolicus (aqMutL) complexed with ATP analogs at 1.69-1.73 Å. The structures revealed significant structural similarities to those of a human MutL homolog, postmeiotic segregation increased 2 (PMS2). We introduced five Lynch syndrome-associated mutations clinically found in human PMS2 into the aqMutL NTD and investigated the protein stability, ATPase activity, and DNA-binding ability of these protein variants. Among the mutations studied, the most unexpected results were obtained for the residue Ser34. Ser34 (Ser46 in PMS2) is located at a previously identified Bergerat ATP-binding fold. We found that the S34I aqMutL NTD retains ATPase and DNA-binding activities. Interestingly, CD spectrometry and trypsin-limited proteolysis indicated the disruption of a secondary structure element of the S34I NTD, destabilizing the overall structure of the aqMutL NTD. In agreement with this, the recombinant human PMS2 S46I NTD was easily digested in the host Escherichia coli cells. Moreover, other mutations resulted in reduced DNA-binding or ATPase activity. In summary, using the thermostable aqMutL protein as a model molecule, we have experimentally determined the effects of the mutations on MutL endonuclease; we discuss the pathological effects of the corresponding mutations in human PMS2.

SUBMITTER: Izuhara K

PROVIDER: S-EPMC7450133 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:ImportanceLynch syndrome is caused by dominantly inherited germline mutations that predispose individuals to colorectal, endometrial, ovarian, and other cancers through inactivation of the cellular mismatch repair system. Lynch syndrome–associated cancers are amenable to surveillance strategies that may improve survival. The age at which surveillance should start is disputed.ObjectiveTo determine whether mutated gene and type of mutation influence age at onset of Lynch syndrome–associated cancers.Design, setting, and participantsA retrospective cohort study of individuals with Lynch syndrome–associated colorectal, endometrial, and/or ovarian cancers whose medical records were included in the clinical database of a large quaternary referral center for genomic medicine in the Northwest of England.ExposuresMutated gene (MLH1, MSH2, MSH6, and/or PMS2) and type of mutation (truncating, splicing, or large rearrangement).Main outcomes and measuresAge at cancer diagnosis.ResultsA total of 1063 individuals with proven Lynch syndrome were included, 495 male and 568 female (mean age 52 years; age range, 10-93 years [children were included in the database, but no children developed cancer]). There were 546 men and women with colorectal cancer, 162 women with endometrial cancer, and 49 women with ovarian cancer; mean follow-up was 68.2 months. Among MLH1 mutation carriers, mutations in MLH1 were associated with colorectal cancer in 249 (61%) of 409 men and women; endometrial cancer in 53 of 196 (27%) women; and ovarian cancer in 15 (8%) of 196 women. Among MSH2 mutation carriers, mutations in MSH2 (the most prevalent mutations overall) were most commonly associated with female-specific cancers: endometrial cancer in 83 (30%) of 279 women; ovarian cancer in 28 (10%) of 279 women; and colorectal cancer in 239 (50%) 479 men and women. Mutations in MSH6 were less prevalent, and MSH6 mutation carriers presented with colorectal and endometrial cancer at later ages than carriers of mutations in MSH2 or MLH1. When stratified by mutation type, women with truncating MLH1 mutations had later ages of onset of endometrial cancer than those with nontruncating mutations (median difference, 6.6 years; 95% CI, 2.7-10.4; P = .002). Carriers of truncating MLH1 mutations presented with colorectal cancer at later ages than those with other mutations, but the difference was not statistically significant.Conclusions and relevanceIndividuals with known Lynch syndrome could be risk stratified by mutated gene and mutation type in tailored surveillance programs. Specifically, individuals with MSH6 mutations could be offered cancer surveillance from a later age. Furthermore, those with truncating MLH1 mutations could begin endometrial cancer surveillance later than those with nontruncating mutations.

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A Lynch syndrome-associated mutation at a Bergerat ATP-binding fold destabilizes the structure of the DNA mismatch repair endonuclease MutL.

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