Lynch Syndrome: Form, Function, Proteins, and Basketball

Protein interaction regions for the human MMR System. The interaction regions between the human MutS homologs (MSH) are shown in blue.⁶ Interactions appear solely between hMSH2 with either hMSH3 or hMSH6 as a heterodimer. The interaction regions between the human MutL homologs (MLH/PMS) are shown in green. Interactions appear solely between hMLH1 with hPMS2, hPMS1, or hMLH3. The interaction regions between the human excision exonuclease hEXOI and the human MSH and MLH/PMS proteins are shown in grey.⁹ The discovery that the human MSH2-MSH6 heterodimer was a primary MSH in MMR engendered the nomenclature of MutSα for this complex.¹⁰ This was soon followed by MutSβ for the human MSH2-MSH3 complex and MutLα for the human MLH1-PMS2 complex, which may also be found as descriptions in the article by Raevaara et al.⁴ Although this contraction clearly saves letter space, it does not appear to be completely descriptive or entirely accurate and has not been used in this review. Biochemical studies have shown that the MLH/PMS heterodimer will only form an active repair complex with the ATP-bound MSH heterodimer sliding clamps¹³ (see http://mmr.med.ohio-state.edu/mmrmovie.html). The binding of ATP by the MLH/PMS heterodimer then appears to stabilize an interaction between hEXOI with the active MSH-MLH/PMS complex to perform the DNA excision step of MMR. The ATP binding domains of both MSH (Walker-like) and MLH/PMS (GHKL-like) proteins are shown in red. Mutations in the ATP binding domains and interaction regions are candidates for loss of function. However, predictions are not always accurate, and the team must be put on the court to assess their ability to play the game together.