title: Probing the pH-dependent structural features of alpha-KTx12.1, a potassium channel blocker from the scorpion Tityus serrulatus.
abstract: Potassium channels are widespread in living cells and are involved in many diseases. The scorpion toxin alpha-KTx(12.1) interacts with various K(+) channels, suggesting its capacity to match diverse channel pores. It is recognized that tissue injuries may affect the pH at toxins site of action, thereby modulating both protein conformation and activity. To better understand its molecular mechanism of action, we studied alpha-KTx(12.1) using pH as a tool to explore its plasticity and NMR in combination with MD calculations to detect it. The toxin solution structure consists of an alpha-helix and a triple-stranded beta-sheet stabilized by four disulfide bridges. The NMR results show, in addition, that His28 possesses an unusually low pK(a) of 5.2. The best set of protein conformers is obtained at pH 4.5, while at pH 7.0, the reduced number of NOEs resulting from a faster hydrogen exchange does not allow to reach a good structural convergence. Nonetheless, MD calculations show that the toxin structure does not vary significantly in that pH range, while conformational changes and modifications of the surface charge distribution occur when His28 is fully protonated. Moreover, essential dynamics analysis reveals variations in the toxin's coherent motions. In conclusion, His28, with its low pK(a) value, provides alpha-KTx(12.1) with the ability to preserve its active conformation over a wide pH interval, thus expanding the range of cellular conditions where the toxin can fully exhibit its activity. Overall, the results further underline the role of histidine as a natural controller of proteins' functionality.
authors.affiliation: Department of Experimental Medicine, Section of Chemistry and Structural Biochemistry, University of Parma, Via Volturno 39, 43100 Parma, Italy.
authors.forename: Sérgio
authors.initials: S
authors.lastname: Oyama
authors.forename: Primoz
authors.initials: P
authors.lastname: Pristovsek
authors.forename: Lorella
authors.initials: L
authors.lastname: Franzoni
authors.forename: Thelma A
authors.initials: TA
authors.lastname: Pertinhez
authors.forename: Eugenia
authors.initials: E
authors.lastname: Schininá
authors.forename: Christian
authors.initials: C
authors.lastname: Lücke
authors.forename: Heinz
authors.initials: H
authors.lastname: Rüterjans
authors.forename: Eliane Candiani
authors.initials: EC
authors.lastname: Arantes
authors.forename: Alberto
authors.initials: A
authors.lastname: Spisni
mesh_terms: D000595:Amino Acid Sequence; D003198:Computer Simulation; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D026902:Potassium Channel Blockers / Q000737:chemistry* / Q000302:isolation & purification; D012604:Scorpion Venoms / Q000737:chemistry*
chemical_list: D026902:Potassium Channel Blockers; D012604:Scorpion Venoms