The telomeric protein Pot1 from Schizosaccharomyces pombe binds ssDNA in two modes with differing 3' end availability.
Bottom Line: These experiments reveal one binding mode characterized by only subtle alternations to the individual OB-fold subdomain structures, resulting in an inaccessible 3' end of the ssDNA.The second binding mode, which has equivalent affinity, interacts differently with the 3' end, rendering it available for interaction with other proteins.These findings suggest a structural switch that contributes to telomere end-protection and length regulation.
Affiliation: Department of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309, USA.Show MeSH
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Mentions: The consistent 1:1 stoichiometry of Pot1-DBD+15mer and the structural similarity of the complex to the individual subdomains suggest a binding mode that fully engages the 3â€² end. This occlusion of the 3â€² Pot1pN-binding site prevents a second Pot1-DBD molecule from binding, unlike the 12mer-binding mode. Indeed, the crystal structure of Pot1pC+9mer reveals an extended aromatic stack involving two amino acid side chains (Trp223 and Tyr224) and two 3â€² bases (G7 and T9) (27) (Figure 5A). Furthermore, based on the conserved chemical shifts in the 15N-HSQC spectra, this structural feature is maintained in the Pot1-DBD+15mer complex (Figure 1).
Affiliation: Department of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309, USA.