http://www.biochemj.org Biochemical Journal - BJ Plant RSS Feed 0264-6021 1470-8728 Biochemical Journal http://www.biochemj.org/images/bj_Name.gif http://www.biochemj.org http://www.biochemj.org/bj/442/0001/bj4420001.htm IDPs (intrinsically disordered proteins) are highly abundant in eukaryotic proteomes and important for cellular functions, especially in cell signalling and transcriptional regulation. An IDR (intrinsically disordered region) within an IDP often undergoes disorder-to-order transitions upon binding to various partners, allowing an IDP to recognize and bind different partners at various binding interfaces. Plant-specific GRAS proteins play critical and diverse roles in plant development and signalling, and act as integrators of signals from multiple plant growth regulatory and environmental inputs. Possessing an intrinsically disordered N-terminal domain, the GRAS proteins constitute the first functionally required unfoldome from the plant kingdom. Furthermore, the N-terminal domains of GRAS proteins contain MoRFs (molecular recognition features), short interaction-prone segments that are located within IDRs and are able to recognize their interacting partners by undergoing disorder-to-order transitions upon binding to these specific partners. These MoRFs represent potential protein–protein binding sites and may be acting as molecular bait in recognition events during plant development. Intrinsic disorder provides GRAS proteins with a degree of binding plasticity that may be linked to their functional versatility. As an overview of structure–function relationships for GRAS proteins, the present review covers the main biological functions of the GRAS family, the IDRs within these proteins and their implications for understanding mode-of-action.

]]> Xiaolin Sun, William T. Jones and Erik H. A. Rikkerink 2012-02-15 doi:10.1042/BJ20111766 Portland Press Ltd. 2012-02-15 http://www.biochemj.org/bj/442/0057/bj4420057.htm The uptake of potassium ions (K⁺) accompanied by an acidification of the apoplasm is a prerequisite for stomatal opening. The acidification (approximately 2–2.5 pH units) is perceived by voltage-gated inward potassium channels (K_in) that then can open their pores with lower energy cost. The sensory units for extracellular pH in stomatal K_in channels are proposed to be histidines exposed to the apoplasm. However, in the Arabidopsis thaliana stomatal K_in channel KAT1, mutations in the unique histidine exposed to the solvent (His²⁶⁷) do not affect the pH dependency. We demonstrate in the present study that His²⁶⁷ of the KAT1 channel cannot sense pH changes since the neighbouring residue Phe²⁶⁶ shifts its pK_a to undetectable values through a cation–π interaction. Instead, we show that Glu²⁴⁰ placed in the extracellular loop between transmembrane segments S5 and S6 is involved in the extracellular acid activation mechanism. Based on structural models we propose that this region may serve as a molecular link between the pH- and the voltage-sensor. Like Glu²⁴⁰, several other titratable residues could contribute to the pH-sensor of KAT1, interact with each other and even connect such residues far away from the voltage-sensor with the gating machinery of the channel.

]]> Wendy González, Janin Riedelsberger, Samuel E. Morales‑Navarro, Julio Caballero, Jans H. Alzate‑Morales, Fernando D. González‑Nilo and Ingo Dreyer 2012-02-15 doi:10.1042/BJ20111498 +-uptake channel KAT1 is built from a sensory cloud rather than from single key amino acids]]> Portland Press Ltd. 2012-02-15