A, The Structure And Function Of Voltage-gated Potassium Ion Channels In The Kv4 N-terminal Fragment Kv4.3n And Channel Regulatory Subunit Kchip1 Protein Complex Analysis Of Two Threonine Phosphate Lyase Spvc Its Substrate Peptide Complex Structure The Ba

First partThe regulatingβsubunits KChIPs and the pore-forming Kv4αsubunits form the native Kv4 channels in brain and heart.To reveal how the KChIPs in the channel complex modulate gating properties of Kv4 channels,we co-expressed Kv4.3 N-terminal domain and KChIP1 and co-crystallized them.The crystal structure of the complex presents a unique clamping form in which a single KChIP1 molecule as a monomer laterally clamps two neighboring Kv4.3 N-terminals in a 4:4 manner,resulting in two contact interfaces that mediate the interaction.The proximal N-terminal inactivation peptide of Kv4.3 is sequestered by its binding to an elongated deep groove on the surface of KChIP1, forming the first contact interface indispensable to the modulation of Kv4.3 by KChIP1,whereas the same KChIP1 molecule through a second interface binds to an adjacent T1 domain of Kv4.3 to stabilize the tetramer of Kv4.3 channels. Biochemical and electrophysilogical results confirm the structural based clamp model of KChIPs modulating Kv4 channels. Second partSpvC is a member of a novel enzyme family designated phosphothreonine lyase that irreversibly inactivates mitogen-activated protein kinases(MAPKs) to interdict host MAPK signaling pathway.To clarify the mechanism of how the enzyme recognizes and removes the activated MAPKs,we crystallized and got the structure of SpvC complexed with a substrate peptide.The structure reveals that the two phosphorylated residues in the peptide predominantly mediate its recognition by SpvC.Substrate binding precipitate conformational changes in SpvC to sequester the phosphothreonine of the substrate peptide in a completely solvent-free environment.Lys136 in SpvC is ideally poised to attack theα-hydrogen orβ-carbon atom of the phosphothreonine for elimination and substitution reactions respectively.Consistently, biochemical assays showed that the SpvC-catalyzed reaction can generate both double bond-containing and covalently linked products.These results uncover the catalytic mechanisms of this family enzyme from different points of view.