Fig. 7: Proposed catalytic mechanism for MUTYH and disrupted mechanism in R241Q and N238S cancer-associated variants. | Nature Communications

Fig. 7: Proposed catalytic mechanism for MUTYH and disrupted mechanism in R241Q and N238S cancer-associated variants.

From: Structure of human MUTYH and functional profiling of cancer-associated variants reveal an allosteric network between its [4Fe-4S] cluster cofactor and active site required for DNA repair

Fig. 7

The adenine excision catalyzed by MUTYH is initiated with the protonation of the adenine by Glu134 which is followed by the glycosidic bond cleavage and formation of an oxacarbenium ion intermediate. Asp236 is proposed to attack the oxacarbenium ion at C1’ to stabilize it by a covalent intermediate. Finally, Glu134 activates a water molecule for nucleophilic attack at C1 to form the AP site product. The structural interplay between the [4Fe-4S] cluster is important for step 2 of catalysis, where Asp236 attacks the oxacarbenium ion. Asp236 has to be oriented near the N-glycosidic bond and deprotonated for the nucleophilic attack. Such orientation and deprotonation status of Asp236 is modulated by the H-bond with Gln238 and allosterically through the [4Fe-4S] cluster via the Cys290-Arg241-Asn238-Asp236 structural bridge. Upon R241Q and N238S mutations the H-bond between Asp236 and Asn238 becomes unstable (cyan dashed arrow) or is broken (black curved lines). With the structural bridge thus compromised the position, protonation state, and charge of catalytic Asp236 position are also impacted (double-headed dashed arrows) with the net consequence of impeding nucleophilic attack of the oxacarbenium ion. This pathological scenario is accompanied by structural instability of the [4Fe-4S] cluster and loss of DNA-MUTYH interactions.

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