Huntingtin N-Terminal Monomeric and Multimeric Structures Destabilized by Covalent Modification of Heteroatomic Residues

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• 作者：James R. Arndt ; Samaneh Ghassabi Kondalaji ; Megan M. Maurer ; Arlo Parker ; Justin Legleiter ; Stephen J. Valentine
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：July 21, 2015
• 年：2015
• 卷：54
• 期：28
• 页码：4285-4296
• 全文大小：500K
• ISSN：1520-4995

文摘

Early stage oligomer formation of the huntingtin protein may be driven by self-association of the 17-residue amphipathic 伪-helix at the protein鈥檚 N-terminus (Nt17). Oligomeric structures have been implicated in neuronal toxicity and may represent important neurotoxic species in Huntington鈥檚 disease. Therefore, a residue-specific structural characterization of Nt17 is crucial to understanding and potentially inhibiting oligomer formation. Native electrospray ion mobility spectrometry鈥搈ass spectrometry (IMS-MS) techniques and molecular dynamics simulations (MDS) have been applied to study coexisting monomer and multimer conformations of Nt17, independent of the remainder of huntingtin exon 1. MDS suggests gas-phase monomer ion structures comprise a helix-turn-coil configuration and a helix-extended-coil region. Elongated dimer species comprise partially helical monomers arranged in an antiparallel geometry. This stacked helical bundle may represent the earliest stages of Nt17-driven oligomer formation. Nt17 monomers and multimers have been further probed using diethylpyrocarbonate (DEPC). An N-terminal site (N-terminus of Threonine-3) and Lysine-6 are modified at higher DEPC concentrations, which led to the formation of an intermediate monomer structure. These modifications resulted in decreased extended monomer ion conformers, as well as a reduction in multimer formation. From the MDS experiments for the dimer ions, Lys6 residues in both monomer constituents interact with Ser16 and Glu12 residues on adjacent peptides; therefore, the decrease in multimer formation could result from disruption of these or similar interactions. This work provides a structurally selective model from which to study Nt17 self-association and provides critical insight toward Nt17 multimerization and, possibly, the early stages of huntingtin exon 1 aggregation.