Spatial Structure and pH-dependent Conformational Diversity of Dimeric Transmembrane Domain of the Receptor Tyrosine Kinase EphA1

Eduard V Bocharov,Maxim L Mayzel,Pavel E Volynsky,Marina V Goncharuk,Yaroslav S Ermolyuk,Alexey A Schulga,Elena O Artemenko,Roman G Efremov,Alexander S Arseniev

doi:10.1074/jbc.m803089200

Eduard V Bocharov, Maxim L Mayzel + Show 7 more

Open Access

https://doi.org/10.1074/jbc.m803089200

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Abstract

Eph receptors are found in a wide variety of cells in developing and mature tissues and represent the largest family of receptor tyrosine kinases, regulating cell shape, movements, and attachment. The receptor tyrosine kinases conduct biochemical signals across plasma membrane via lateral dimerization in which their transmembrane domains play an important role. Structural-dynamic properties of the homodimeric transmembrane domain of the EphA1 receptor were investigated with the aid of solution NMR in lipid bicelles and molecular dynamics in explicit lipid bilayer. EphA1 transmembrane segments associate in a right-handed parallel alpha-helical bundle, region (544-569)(2), through the N-terminal glycine zipper motif A(550)X(3)G(554)X(3)G(558). Under acidic conditions, the N terminus of the transmembrane helix is stabilized by an N-capping box formed by the uncharged carboxyl group of Glu(547), whereas its deprotonation results in a rearrangement of hydrogen bonds, fractional unfolding of the helix, and a realignment of the helix-helix packing with appearance of additional minor dimer conformation utilizing seemingly the C-terminal GG4-like dimerization motif A(560)X(3)G(564). This can be interpreted as the ability of the EphA1 receptor to adjust its response to ligand binding according to extracellular pH. The dependence of the pK(a) value of Glu(547) and the dimer conformational equilibrium on the lipid head charge suggests that both local environment and membrane surface potential can modulate dimerization and activation of the receptor. This makes the EphA1 receptor unique among the Eph family, implying its possible physiological role as an "extracellular pH sensor," and can have relevant physiological implications.

Highlights

Like other receptor tyrosine kinases, both types of Erythropoietin-producing hepatocellular (Eph) receptors contain a single transmembrane (TM) helical domain with an N-terminal glycosylated extracellular region comprised of a ligand-binding domain with immunoglobulin-like motifs, a cysteine-rich region with an epidermal growth factor-like motif, and two fibronectin type III repeats
Accumulating evidences reveal that the proper lateral dimerization of TM domains of receptor tyrosine kinase members is required for biochemical signal transduction across plasma membrane [16, 17]
Consistent with this notion and with the fact that Eph-ephrin signaling requires lateral dimerization or aggregation in cell membrane [2, 6, 12, 20], we present the high resolution spatial structure of the homodimeric TM domain of the human EphA1 receptor obtained by heteronuclear NMR in lipid bicelles combined with molecular dynamics (MD) relaxation in explicit membrane

Summary

Introduction

Like other receptor tyrosine kinases, both types of Eph receptors contain a single transmembrane (TM) helical domain with an N-terminal glycosylated extracellular region comprised of a ligand-binding domain with immunoglobulin-like motifs, a cysteine-rich region with an epidermal growth factor-like motif, and two fibronectin type III repeats. The found dimerization specificity and dependence of structural-dynamic properties of the EphA1 TM domain on ionization state of the membrane embedded glutamate carboxyl group tempted us to speculate how extracellular conditions and local cell membrane environment can modulate biological activity of the receptor, providing a better understanding of the molecular mechanism of the Eph-ephrin signaling.

Results

Conclusion