Structural element responsible for the Fe(III)–phytosiderophore specific transport by HvYS1 transporter in barley

Abstract 

Hordeum vulgare L. yellow stripe 1 (HvYS1) is a selective transporter for Fe(III)–phytosiderophores, involved in primary iron acquisition from soils in barley roots. In contrast, Zea mays yellow stripe 1 (ZmYS1) in maize possesses broad substrate specificity, despite a high homology with HvYS1. Here we revealed, by assessing the transport activity of a series of HvYS1–ZmYS1 chimeras, that the outer membrane loop between the sixth and seventh transmembrane regions is essential for substrate specificity. Circular dichroism spectra indicated that a synthetic peptide corresponding to the loop of HvYS1 forms an α-helix in solution, whereas that of ZmYS1 is flexible. We propose that the structural difference at this particular loop determines the substrate specificity of the HvYS1 transporter.

Abbreviations: HvYS1, Hordeum vulgare L. yellow stripe 1, ZmYS1, Zea mays yellow stripe 1, YSL, yellow stripe 1-like, MA, mugineic acid, DMA, 2′-deoxymugineic acid, NA, nicotianamine, CD, circular dichroism

Keywords: Chimera, α-helix, Iron acquisition, Iron–phytosiderophore, Substrate specificity, Transporter