Analysis of AtHIRD11 Intrinsic Disorder and Binding Towards Metal Ions by Capillary Gel Electrophoresis and Affinity Capillary Electrophoresis

Summary

This protocol combines the characterization of a protein sample by capillary gel electrophoresis and a fast-binding screening for charged ligands by affinity capillary electrophoresis. It is recommended for proteins with a flexible structure, such as intrinsically disordered proteins, to determine any differences in binding for different conformers.

Abstract

Plants are strongly dependent on their environment. In order to adjust to stressful changes (e.g., drought and high salinity), higher plants evolve classes of intrinsically disordered proteins (IDPs) to reduce oxidative and osmotic stress. This article uses a combination of capillary gel electrophoresis (CGE) and mobility shift affinity electrophoresis (ACE) in order to describe the binding behavior of different conformers of the IDP AtHIRD11 from Arabidopsis thaliana. CGE is used to confirm the purity of AtHIRD11 and to exclude fragments, posttranslational modifications, and other impurities as reasons for complex peak patterns. In this part of the experiment, the different sample components are separated by a viscous gel inside a capillary by their different masses and detected with a diode array detector. Afterward, the binding behavior of the sample towards various metal ions is investigated by ACE. In this case, the ligand is added to the buffer solution and the shift in migration time is measured in order to determine whether a binding event has occurred or not. One of the advantages of using the combination of CGE and ACE to determine the binding behavior of an IDP is the possibility to automate the gel electrophoresis and the binding assay. Furthermore, CGE shows a lower limit of detection than the classical gel electrophoresis and ACE is able to determine the manner of binding a ligand in a fast manner. In addition, ACE can also be applied to other charged species than metal ions. However, the use of this method for binding experiments is limited in its ability to determine the number of binding sites. Nevertheless, the combination of CGE and ACE can be adapted for characterizing the binding behavior of any protein sample towards numerous charged ligands.

Introduction

Plants are more dependent on their environment than many other life forms. Since plants cannot move to other places, they have to adjust to changes in their surroundings (e.g., drought, cold and high salt concentrations). Consequently, higher plants developed specialized stress proteins like dehydrins, which fulfill manifold tasks to reduce cell stress related to high salinity. These proteins bind water and ions inside cells, reduce oxidative stress by binding Cu²⁺-ions, and interact with phospholipids as well as the cytoskeletons. Moreover, binding Zn²⁺-ions allows these proteins to act as transcription factors. Their ability to bind Ca....

Protocol

1. Preparation of the Capillary Electrophoresis Instruments

1. Prepare the capillaries
   1. Use a glass cutter to cut a bare-fused silica capillary with a polyimide external coating and an inner diameter of 50 µm into 33 cm (for the CGE experiment) and 30 cm (for the ACE experiment) long capillaries. Perform the cutting on a glass plate.
      Note: The 2 different experimental setups were developed for 2 different instruments. In order to use them on other instruments, a proper method transfer has to be performed and the capillary length has to be adjusted to the allowed length of the instrument.
   2. Use a pen to mark th....

Results

Figure 1 shows the electropherogram for the AtHIRD11 sample obtained during the CGE experiments. The peptide size increases from left to right. Peak number 4 has the largest mass and indicates the intact protein. The smaller peaks 2 and 3 represent smaller impurities (e.g., degradation products). The first peak and the inconsistency of the baseline before could also be reproduced without the protein sample. Therefore, it is related to the SDS gel its.......

Discussion

For all CE experiments, the preparation of the capillary is a critical step. Since it is a glass tube with a small diameter, it can easily break at the spots where the coating is removed when it is being handled. The installation of the capillary into the instrument should be done very carefully.

The critical steps involved in using the ACE method mainly pertain to the experimental setup. Another critical step is finding the right sample injection parameters. The injected amount of the sample .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
AtHIRD11 sample	Shizuoka University (Group Prof. M. Hara)	-	Dehydrin Protein from Arabidopsis thaliana expressed in Escherichia coli
Barefused silica capillary	Polymicro Technologies (Phoenix, USA)	106815-0017	TSP050375, 50 μm inner diameter, 363 μm outer diameter, polyimide coating
Agilent 1600A	Agilent Technologies (Waldbronn, Germany)	comercially not available anymore	Capillary electrophoresis instrument; Agilent 7100 CE can be used instead
Agilent 7100 CE	Agilent Technologies (Waldbronn, Germany)	G7100A	Capillary electrophoresis instrument
Injekt 2 mL	B. Braun (Melsungen, Germany)	4606051V	Syringe for filtration
Rotilabo-syringe filters	Carl Roth GmbH + Co. KG (Karlsruhe, Germany)	KY62.1	PVDF membrane filter for solution filtration
Eppendorf Research plus 10 μL	Eppendorf (Wesseling-Berzdorf, Germany)	3121 000.023	Micro pipette for sample handling
Eppendorf Research plus 10 μL	Eppendorf (Wesseling-Berzdorf, Germany)	3121 000.120	Micro pipette for handling the ligand solutions
Bulb pipette 10 mL	Duran Group GmbH(Mainz, Germany)	24 338 08	Preparing theNaOH solution
Bulb pipette 25 mL	Duran Group GmbH(Mainz, Germany)	24 338 14	Preparing the ligand solution
Duran glas volumetric flask 25 mL	Duran Group GmbH(Mainz, Germany)	24 671 1457	Preparing the ligand stock solution
Duran glas volumetric flask 10 mL	Duran Group GmbH(Mainz, Germany)	24 671 1054	Preparing the ligand stock solution
Proteome Lab SDS MW Gel Buffer	Beckman Coulter (Brea, USA)	comercially not available anymore	Separation during capillary gel electrophoresis / Alternative SDS buffer: CE-SDS run buffer from Bio-Rad Laboratories (München, Germany) Catalog Number: 1485032
Acetanilide	Sigma-Aldrich (Steinheim, Germany)	397229-5G	Electroosmotic flow marker
Manganese(II) chloride	Sigma-Aldrich (Steinheim, Germany)	13217	Ligand
Ethylenediaminetetraacetic acid (EDTA)	Sigma-Aldrich (Steinheim, Germany)	431788-100G	Rinsing ingredient
Bariumchloride	Sigma-Aldrich (Steinheim, Germany)	202738-5G	Ligand
Sodium dodecyl sulfate	Sigma-Aldrich (Steinheim, Germany)	71729-100G	Solublizing protein for capillary gel electrophoresis
Nickel(II) chloride hexahydrate	Sigma-Aldrich (Steinheim, Germany)	654507-5G	Ligand
Selenium(IV) chloride	Sigma-Aldrich (Steinheim, Germany)	323527-10G	Ligand
2-amino-2-hydroxy-methylpropane-1.3-diol (Tris)	Sigma-Aldrich (Steinheim, Germany)	252859-100G	Buffer ingredient
Zinc(II) chloride	Merck Millipore ( Darmstadt, Germany)	1088160250	Ligand
Strontium nitrate	Merck Millipore ( Darmstadt, Germany)	1078720250	Ligand
Calcium chloride dihydrate	Merck Millipore ( Darmstadt, Germany)	1371015000	Ligand
37% hydrochloric acid	Merck Millipore ( Darmstadt, Germany)	1003171000	Adjusting pH
Copper(II) chloride dihydrate	Riedel-de Haën (Seelze, Germany)	31286	Ligand
Sonorex Longlife RK 1028 CH 45L	Allpax (Papenburg, Germany)	10000084;0	Ultrasonic bath
Agilent ChemStation Rev. 8.04.03-SP1	Agilent Technologies (Waldbronn, Germany)	G2070-91126	Software packages to operate the CE instruments, acquisite data and evaluate it