Self-association of the Escherichia coliTranscription Activator MalT in the Presence of Maltotriose and ATP

Valérie Schreiber,Evelyne Richet

doi:10.1074/jbc.274.47.33220

Abstract

MalT, the transcriptional activator of the Escherichia coli maltose regulon, binds the MalT-dependent promoters and activates transcription initiation only in the presence of maltotriose and ATP (or adenylyl imidodiphosphate (AMP-PNP)). Cooperative binding of MalT to the array of cognate sites present in the MalT-dependent promoters suggests that promoter binding involves MalT oligomerization. Gel filtration and sedimentation experiments were used to analyze the quaternary structure of MalT in solution in the absence or presence of maltotriose and/or AMP-PNP, ATP, or ADP. The protein is monomeric in the absence of ligands and in the presence of ADP. In the presence of maltotriose, AMP-PNP, or ATP only, the protein self-associates, but a large fraction of the protein remains monomeric. In the presence of both maltotriose and AMP-PNP (ATP or ADP), the protein is essentially oligomeric, with the difference being that the oligomerization is less favored in the presence of ADP + maltotriose than in the presence of AMP-PNP + maltotriose. We present evidence that the association pathway comprises the following steps: monomers --> dimers --> (MalT)(n) --> aggregates, where 3 </= n </= 6. From these data, we conclude that the role of maltotriose and ATP as positive effectors is to induce the multimerization of MalT, and hence its cooperative binding to the mal promoters.

Highlights

The transcriptional activator material in the (MalT) plays a key role in the regulation of expression of the Escherichia coli maltose regulon that encodes proteins involved in the uptake and catabolism of maltodextrins
Ligand-induced Self-association of MalT—The results of the gel filtration and sedimentation experiments reported in this paper reveal several features of the association state of MalT in the absence or presence of its effectors, maltotriose and ATP
Such a model accounts for the three peaks observed by gel filtration in the presence of maltotriose alone, the two discrete peaks corresponding to the dimer and the monomer and the early peak, which first appears at 600 kDa and the apparent molecular mass of which increases as the concentration of MalT is raised

Summary

Introduction

The transcriptional activator MalT plays a key role in the regulation of expression of the Escherichia coli maltose regulon that encodes proteins involved in the uptake and catabolism of maltodextrins. That MalT is monomeric at 1 ␮M in the presence of maltotriose is consistent with the observation that at low concentration, MalT has a sedimentation coefficient s20,w of 5.9 S, which corresponds to that of an Ϸ110-kDa globular protein (Fig. 3B).

Results

Conclusion