ATP binding/ATPase activity of MutS

Compare your draft descriptions of MutS domains with this MutS Chime Tutorial (Stofgren & Marcey 2001, California Lutheran University)

ATP binding/ATPase activity of MutS

Devon, Amar, Jessie, Priscilla

The nucleotide binding motifs (N-1, -2, -3, and 3’) are located near the dimer interface region of domain V. The ATP binding site is located at a sulphate ion hydrogen bonded to N-1. N-2 potentially binds the gamma-phosphate of ATP. This combination suggests that ATP is bound by a combination of the subunits, however they also refer to the “ATP binding site of the neighboring subunit,” implying that each subunit has a unique binding site. Figure 3C shows two sulphate ions, one on each subunit, which also suggests that each subunit has a unique binding site. The active site is located at the dimer interface, and hydrolysis of ATP requires the dimer. ATP is not shown in any figures in this paper, making it difficult to determine the exact nature of ATP binding.

Shawn, Andrew,Michael, Alby

The MutS domain V contains residues that can bind ATP, but the activity of ATP binding is composite between two members of the MutS dimer. It is suggested that the affinity of MutS for MutH is increased due to ATP binding, which causes allosteric changes in the molecule.

Lesion Recognition:

Group 3: Ann, Anna, Brian, Alexis

Phe39 of Domain I of Mut S’s subunit A approaches the minor groove on the 3’side. The ring of Phe39 ring stacks with the unpaired T’s aromatic rings. The-sheet of Domain I Subunit A contacts 9 nucleotides betweenphosphate backbones in the minor groove, which has been widened due to thekinking of DNA as a result of contact with the MutS dimer. A -hairpinis anchored on the outside of this domain via the -sheet interaction. Additionally, a hydrogen bond forms between the Glutamate 41 side chain and themismatched T.The interactions between Phe39 and the unpaired T, result in DNA kinking towardsthe major groove. The kink is stabilized by interactions with domains I and IVof both subunits. Each domain surrounds 5-8bp on either side of the kink. Domain IV uses β-turns of two β-sheets [This is not complete because we ran out of time]

Group 6:

The unpaired T is pushed towards the minor groove and is stabilized by a hydrogen bond by O4 oxygen and N2 of the 5’G. This conformation of T is also stabilized by interactions with mutS. The first interaction is a hydrogen bond with the side chain of Glu 41. The second interaction is aromatic ring stacking with Phe 39 which approaches the DNA from the minor groove. As a consequence of the base stacking interaction from the minor groove, the major groove is sharply kinked and the minor groove is widened. The mutS-DNA interactions are generally non-sequence specific because most contact is made with the sugar-phosphate backbone. The lesion is initially recognized because of the irregular topology of the DNA at the site of the mismatch.