γ‐Secretase cleavage of the Alzheimer risk factor TREM 2 is determined by its intrinsic structural dynamics

Abstract

Sequence variants of the microglial expressed TREM2 (triggering receptor expressed on myeloid cells 2) are a major risk factor for late onset Alzheimer's disease. TREM2 requires a stable interaction with DAP12 in the membrane to initiate signaling, which is terminated by TREM2 ectodomain shedding and subsequent intramembrane cleavage by c-secretase. To understand the structural basis for the specificity of the intramembrane cleavage event, we determined the solution structure of the TREM2 transmembrane helix (TMH). Caused by the presence of a charged amino acid in the membrane region, the TREM2-TMH adopts a kinked structure with increased flexibility. Charge removal leads to TMH stabilization and reduced dynamics, similar to its structure in complex with DAP12. Strikingly, these dynamical features match with the site of the initial c-secretase cleavage event. These data suggest an unprecedented cleavage mechanism by c-secretase where flexible TMH regions act as key determinants of substrate cleavage specificity.

High‐resolution analysis of the conformational transition of pro‐apoptotic Bak at the lipid membrane

“…However, a high‐resolution structure was not yet available. For high‐level production in E. coli , the Bak‐TMH was produced as an N‐terminal fusion protein with the expression helper and solubility tag GB1 (Zhou & Wagner, 2010), similar to what has previously been reported for the BclxL‐TMH and other systems (Raltchev et al , 2018; Steiner et al , 2020). Using multidimensional NMR experiments, we obtained backbone resonance assignments of 89% of all non‐proline residues in the Bak‐TMH protein construct both in dodecylphosphocholine (DPC) micelles (Appendix Fig S1A) and in DMPC/DMPG (3:1) MSP1D1ΔH5 nanodiscs (Hagn et al , 2013, 2018; Klöpfer & Hagn, 2019) (Fig 2B).…”

NMR Structural and Biophysical Analysis of the Disease-Linked Inner Mitochondrial Membrane Protein MPV17

“…Nanodiscs were assembled with the MPV17 to MSP ratios indicated for the individual assemblies according to established protocols [19][20][21]. ΔH5-nanodiscs were formed by applying an MSP to lipid ratio of 1:25 [31], while 1E3D1-nanodiscs were formed using an MSP to lipid ratio of 1:85 (80 for the 1:1 ratio of MPV17:MSP) [25]. As lipids either DMPC/DMPG (75/25) or DMPC/Cardiolipin (14:1) (80/20) were used.…”

Triggering Receptor Expressed on Myeloid Cells 2 Protects Dopaminergic Neurons by Promoting Autophagy in the Inflammatory Pathogenesis of Parkinson’s Disease

“…It contains a long extracellular domain that regulates the function of microglia by stably interacting with DAP12 in the membrane and initiating the interaction between the signal transduction machinery and the extracellular environment (Konishi and Kiyama, 2018). The signal is terminated by TREM2 ectodomain shedding and subsequent intramembrane cleavage by γ-secretase (Steiner et al, 2020).…”