Pyridoxamine is a substrate of the energy-coupling factor transporter HmpT

Tingliang Wang,Hang Yin,Yigong Shi,Armando Jerome De Jesus

doi:10.1038/celldisc.2015.14

Abstract

Energy-coupling factor (ECF) transporters belong to a novel family of proteins that forms a subset within the ATP-binding cassette (ABC) transporter family. These proteins are responsible for the uptake of micronutrients in bacteria. ECF transporters are composed of four proteins: the A- and A′-components, the T-component and the S-component. One of the ECF transporters, named HmpT, was crystallized in the apo form with all four components. It is currently unknown whether HmpT serves as a transporter for hydroxymethyl pyrimidine or the different forms of vitamin B6 (pyridoxine, pyridoxal or pyridoxamine). Using a combination of molecular dynamics (MD) simulations and mass spectrometry, we have identified pyridoxamine to be the preferred substrate of HmpT. Mass spectra show that the mass of the substrate from the HmpT–substrate complex matches that of pyridoxamine. MD simulations likewise indicate that pyridoxamine interacts most strongly with most of the conserved residues of the S-component (Glu 41, His 84 and Gln 43) compared with the other vitamin B6 forms. Furthermore, the simulations have implied that loops 1 and 5 of the S-component can participate in the gating action for HmpT.

Highlights

As early as the late 1970s, proteins that transport B-vitamins into bacteria have been observed [1,2,3], but it was only recently that these proteins, designated as energy-coupling factor (ECF) transporters, have been identified to form a novel subset within the ATPbinding cassette (ABC) transporter family [4,5,6,7,8,9]
Mass spectra identifies pyridoxamine as the substrate extracted from HmpT
One overarching question in studying the HmpT transporter remains to be the identification of its substrate due to the fact that the ECF structure of which HmpT is a part was crystallized in its apo form

Summary

Introduction

As early as the late 1970s, proteins that transport B-vitamins into bacteria have been observed [1,2,3], but it was only recently that these proteins, designated as energy-coupling factor (ECF) transporters, have been identified to form a novel subset within the ATPbinding cassette (ABC) transporter family [4,5,6,7,8,9]. For further exploration of the interaction of the identified substrate with the binding pocket, molecular dynamics (MD) simulation is employed to model HmpT in a membrane environment.

Results

Conclusion