title: Site directed mutagenesis of StSUT1 reveals target amino acids of regulation and stability.
abstract: Plant sucrose transporters (SUTs) are functional as sucrose-proton-cotransporters with an optimal transport activity in the acidic pH range. Recently, the pH optimum of the Solanum tuberosum sucrose transporter StSUT1 was experimentally determined to range at an unexpectedly low pH of 3 or even below. Various research groups have confirmed these surprising findings independently and in different organisms. Here we provide further experimental evidence for a pH optimum at physiological extrema. Site directed mutagenesis provides information about functional amino acids, which are highly conserved and responsible for this extraordinary increase in transport capacity under extreme pH conditions. Redox-dependent dimerization of the StSUT1 protein was described earlier. Here the ability of StSUT1 to form homodimers was demonstrated by heterologous expression in Lactococcus lactis and Xenopus leavis using Western blots, and in plants by bimolecular fluorescence complementation. Mutagenesis of highly conserved cysteine residues revealed their importance in protein stability. The accessibility of regulatory amino acid residues in the light of StSUT1's compartmentalization in membrane microdomains is discussed.
authors: Humboldt University of Berlin, Department of Plant Physiology, Philippstr. 13, Building 12, 10115 Berlin, Germany; University of Zurich, Institute of Plant Biology, Zollikerstr. 107, CH-8008 Zurich, Switzerland(1).
authors: Undine
authors: U
authors: Krügel
authors: Elena
authors: E
authors: Wiederhold
authors: Jelena
authors: J
authors: Pustogowa
authors: Aleksandra
authors: A
authors: Hackel
authors: Bernhard
authors: B
authors: Grimm
authors: Christina
authors: C
authors: Kühn
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000235:genetics*; D000818:Animals; D018506:Gene Expression Regulation, Plant; D006863:Hydrogen-Ion Concentration; D013294:Lactococcus lactis; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000096:biosynthesis* / Q000737:chemistry* / Q000235:genetics; D055550:Protein Stability; D011198:Solanum tuberosum; D014982:Xenopus laevis
chemical_list: D000596:Amino Acids; D026901:Membrane Transport Proteins; D010940:Plant Proteins; C078729:sucrose transport protein, plant
keywords: Homodimerization; Membrane microdomains; Regulation of sucrose transport; Site-directed mutagenesis