Molecular Dynamics simulations of Alzheimer's variants, R47H and R62H, in TREM2 provide evidence for structural alterations behind functional changes

Abstract

There is strong evidence supporting the association between Alzheimers disease (AD) and protein-coding variants, R47H and R62H in TREM2. The TREM2 protein is an immune receptor found in brain microglia. A structural alteration could therefore have a large effect on the protein. Crystallised structures were used as a base for both WT and mutated proteins. These subjected to 300ns of molecular dynamic simulation (MD). Results suggest structural alterations in both mutated forms of TREM2. A large change was noted in the R47H simulation in the complementarity-determining region two (CDR2) binding loop, a proposed binding sites for ligands such as APOE, a smaller change was observed in the R62H model. These differing levels of structural impact could explain the in vitro observed differences in TREM2-ligand binding. Author SummaryA number of mutations have been found in the TREM2 protein in populations of people with Alzheimers and other dementias. Two of these mutations are similar in that the both cause the same coding change in the same domain of the protein. However, they both cause a very different result in terms of risk and in vitro observed changes. Why these two similar mutations are so different is largely unknown. Here we have used a in silico, simulation, approach to understanding the structural changes which occur in both of the mutations. Our results suggest that the mutation which carries a higher risk, but it less commonly observed, has a much larger impact on the protein structure than the mutation which is thought to be less damaging. This structural change is observed at a part of the protein which is thought to code for a binding loop and a change here could have a big impact on the proteins function. Further studies to investigate this binding loop could help not only a better understanding of TREM2s role in the onset of dementia but also possibly provide a target for therapeutics.