The influence of various regions of the FOXP2 sequence on its structure and DNA-binding function.

Monare Thulo,Megan A Rabie,Ashleigh A Blane,Naadira Pahad,J Carlos Penedo,Sylvia Fanucchi,Cardon M Perumal,Heather L Donald

doi:10.1042/bsr20202128

Monare Thulo, Megan A Rabie + Show 6 more

Open Access

https://doi.org/10.1042/bsr20202128

Copy DOI

Abstract

FOX proteins are a superfamily of transcription factors which share a DNA-binding domain referred to as the forkhead domain. Our focus is on the FOXP subfamily members, which are involved in language and cognition amongst other things. The FOXP proteins contain a conserved zinc finger and a leucine zipper motif in addition to the forkhead domain. The remainder of the sequence is predicted to be unstructured and includes an acidic C-terminal tail. In the present study, we aim to investigate how both the structured and unstructured regions of the sequence cooperate so as to enable FOXP proteins to perform their function. We do this by studying the effect of these regions on both oligomerisation and DNA binding. Structurally, the FOXP proteins appear to be comparatively globular with a high proportion of helical structure. The proteins multimerise via the leucine zipper, and the stability of the multimers is controlled by the unstructured interlinking sequence including the acid rich tail. FOXP2 is more compact than FOXP1, has a greater propensity to form higher order oligomers, and binds DNA with stronger affinity. We conclude that while the forkhead domain is necessary for DNA binding, the affinity of the binding event is attributable to the leucine zipper, and the unstructured regions play a significant role in the specificity of binding. The acid rich tail forms specific contacts with the forkhead domain which may influence oligomerisation and DNA binding, and therefore the acid rich tail may play an important regulatory role in FOXP transcription.

Highlights

The forkhead box (FOX) superfamily comprises one of the largest classes of transcription factors, consisting of over 100 members in species ranging from yeast to humans
They were: FOXP1 LZ-END and FOXP2 LZ-END which contained the full stretch of sequence from the leucine zipper to the C-terminal end of the protein in both FOXP1 (UniProt ID Q9H334) and FOXP2 (UniProt ID O15409) respectively; FOXP2 LZ-FHD which contained the stretch of FOXP2 sequence from the leucine zipper to the end of the forkhead domain; FOXP2 FHD which contained the isolated forkhead domain and FOXP2 FHD-END which contained FOXP2 sequence from the beginning of the forkhead domain to the end of the protein including the acidic C-terminal tail
The FOXP domains as well as the unstructured interlinking sequence have precise significant roles to play in the function of these proteins, in terms of oligomerisation and DNA binding

Summary

Introduction

The FOX superfamily comprises one of the largest classes of transcription factors, consisting of over 100 members in species ranging from yeast to humans. This multimerisation event can be homomeric but can be heteromeric and different members of the FOXP family have been shown to hetero-associate [5,21,22,23] Unlike their FOX siblings which interact with DNA as monomers, it has been stated that it is necessary for FOXP proteins to dimerise via the leucine zipper in order to interact with DNA [5]. While there is some evidence already available to suggest putative roles for certain parts of the sequence (e.g., the polyglutamine tract and zinc finger motif are believed to be involved in protein–protein associations, the leucine zipper has been shown to cause homo and heterotypic multimerisation and the forkhead domain is responsible for DNA-binding specificity [5,19,25]), it is not known how these domains, along with the remaining undefined regions of the sequence including the acid rich tail, function together to support a cohesive mechanism of transcriptional regulation. The objective of the present study, is to provide more clarity on how the two oligomerisation interfaces, the leucine zipper and the forkhead domain, as well as the interlinking disordered sequence including the acid rich tail, co-operate so as to contribute to the structure and DNA binding of the FOXP proteins

Objectives

Methods

Results

Discussion

Conclusion