An ACT-like Domain Participates in the Dimerization of Several Plant Basic-helix-loop-helix Transcription Factors

Antje Feller,J Marcela Hernandez,Erich Grotewold

doi:10.1074/jbc.m603262200

Antje Feller, J Marcela Hernandez + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m603262200

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Abstract

The maize basic-helix-loop-helix (bHLH) factor R belongs to a group of proteins with important functions in the regulation of metabolism and development through the cooperation with R2R3-MYB transcription factors. Here we show that in addition to the bHLH and the R2R3-MYB-interacting domains, R contains a dimerization region located C-terminal to the bHLH motif. This protein-protein interaction domain is important for the regulation of anthocyanin pigment biosynthesis by contributing to the recruitment of the C1 R2R3-MYB factor to the C1 binding sites present in the promoters of flavonoid biosynthetic genes. The R dimerization region bares structural similarity to the ACT domain present in several metabolic enzymes. Protein fold recognition analyses resulted in the identification of similar ACT-like domains in several other plant bHLH proteins. We show that at least one of these related motifs is capable of mediating homodimer formation. These findings underscore the function of R as a docking site for multiple protein-protein interactions and provide evidence for the presence of a novel dimerization domain in multiple plant bHLH proteins.

Highlights

Unique ways to their regulatory function [8]
This group is shared by the Arabidopsis GL3 (GLABROUS3), EGL3 (ENHANCER OF GLABROUS3), TT8 (TRANSPARTENT TESTA8) and AtMYC1 proteins, which participate in trichome and root hair formation and in the control of flavonoid pigments [21,22,23,24,25], functions that can be complemented by the maize R gene, Lc [26]
The dimerization region of R is C-terminal to the bHLH motif and has structural similarity to the ACT domain involved in the allosteric regulation of many amino acid metabolic enzymes

Summary

Introduction

Unique ways to their regulatory function [8]. For example, the Myc proto-oncoprotein forms heterodimers with Max through the respective bHLH and adjacent basic leucine zipper (bZip) domains [9]. Based on the sequence homology of the bHLH domain and the presence of conserved N-terminal regions, R belongs to group IIIf of the plant bHLH gene family [3] This group is shared by the Arabidopsis GL3 (GLABROUS3), EGL3 (ENHANCER OF GLABROUS3), TT8 (TRANSPARTENT TESTA8) and AtMYC1 proteins, which participate in trichome and root hair formation and in the control of flavonoid pigments [21,22,23,24,25], functions that can be complemented by the maize R gene, Lc [26]. Structural homology searches identified other bHLH factors with similar ACT domains, and we show that at least one of them can mediate the formation of specific dimers These findings highlight the role of a novel dimerization domain for the R regulatory activity and provide evidence for the recruitment by eukaryotic transcription factors of protein-protein interaction domains characteristic of metabolic enzymes

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