Off-campus UMass Amherst users: To download campus access dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Dissertations that have an embargo placed on them will not be available to anyone until the embargo expires.

Date of Award

9-2010

Document Type

Campus Access

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Molecular and Cellular Biology

First Advisor

Christopher L. Woodcock

Second Advisor

Lila M. Gierasch

Third Advisor

Craig T. Martin

Subject Categories

Biochemistry | Biophysics | Molecular Biology

Abstract

Methyl CpG binding protein 2 (MeCP2) is a methylated DNA binding protein which, when mutated, leads to a severe neurodevelopmental disorder known as Rett syndrome (RTT). In the present work I have shown that MeCP2 is a highly unstructured protein with modular organization and harbors nine interspersed alpha-molecular recognition features (alpha-MoRFs). A detailed domain by domain analysis of the properties of human MeCP2 domains has revealed that MeCP2 binding to DNA is characterized by disorder-to-order transition and binding-dependent conformational selection. I have shown that in addition to the core Methyl-CpG Binding Domain (MBD), MeCp2 contains a chromatin (histone) binding domain, several autonomous DNA binding domains as well as domains which allosterically regulate DNA binding. Concerted binding through these domains lead to unprecedented chromatin compaction as well as nucleosome array oligomerization. Using a variety of biochemical, biophysical and imaging techniques, I have established the differences in physical principles driving both nonspecific and methyl-selective MeCP2 binding to DNA. Both binding modes are DNA length dependent. Even though MeCP2 exists as a monomer in solution, equilibrium exists between monomers and dimers on DNA. Consecutive interactions of MeCP2 monomers with DNA are cooperative, a property strongly correlated with methylation density and the presence of symmetric repeats of A/T stretches. Cooperativity in binding is abolished if the C-terminus of the protein is truncated and also in the severe RTT mutant F155S. I have also shown that Rett Syndrome-causing mutations in human MeCP2 result in diverse structural changes that impact folding, conformational coupling between domains and DNA interactions. The MeCP2 binding site on the nucleosome overlaps with that of linker histone H1 and is proximal to histone H3 at the nucleosomal dyad. MeCP2 mediated changes in nucleosome architecture result in compaction resembling the classical zigzag motif induced by histone H1, considered important for 30nm fiber formation. In vivochromatin binding kinetics and in vitro steady state nucleosome binding of both MeCP2 and H1 provide strong evidence for competition between MeCP2 and H1 for common binding sites. This suggests that chromatin binding by MeCP2 and H1 in vivo should be viewed in the context of competitive multifactorial regulation.

Share

COinS