Binding studies of the FOXP2 forkhead domain and its cognate DNA sequences
Date
2016
Authors
Webb, Helen Susannah
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Abstract
FOXP2 is the gene product of the so-called “language gene” and is the only
protein known to be involved in a monogenetic autosomally inherited language
disorder. This disorder has been termed Speech-Language Disorder 1. In addition
to the role it plays in language, FOXP2 is thought to be involved in cancer, autism
and schizophrenia. FOXP2 is a member of the P subfamily of FOX transcription
factors, the DNA-binding domain of which is the forkhead domain. The aim of
this work was to investigate the binding mechanism of the FOXP2 forkhead
domain and various DNA sequences in order to assess affinity and specificity. It
was shown by surface plasmon resonance that the FOXP2 forkhead domain can
recognise a variety of DNA sequences, including a novel sequence, identified by
systematic evolution of ligands by exponential enrichment. This motif has not
previously been reported as a binding motif of the FOXP2 forkhead domain.
Kinetic analysis by surface plasmon resonance showed that the novel sequence, as
well as other published cognate sequences, each binds to the FOXP2 forkhead
domain with different rates and affinities. Molecular docking of the DNA
sequences to the FOXP2 forkhead domain revealed that electrostatic interactions
between positively charged amino acids and the DNA backbone, as well as basespecific
interactions between His554 and the DNA appear to be key in
determining rates and affinities of binding interactions of the FOXP2 forkhead
domain and DNA. Based on these findings, three types of DNA-binding are
proposed for the FOXP2 forkhead domain. These types are: low affinity, nonfunctional
binding; moderate affinity, non-functional binding and high affinity,
functional binding. It is probable that each type of binding serves to control the
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spatial location of the protein within the nucleus, as well as the local concentration
of protein. The proposed mechanism of binding for the forkhead domain of
FOXP2 may have a future impact on the binding and function of full length
FOXP2.
Description
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015.