Identification of Potential Interacting Proteins With the Extracellular Loops of the Neuronal Glycoprotein M6a by TMT/MS

Abstract

Aparicio et al. TMT/MS Unveils Key M6a Interactors the surface of oligodendrocytes. Indeed, we demonstrated the (cis and trans) interaction between M6a and proteolipid protein (PLP) in neuroblastoma N2a cells. Finally, the 72 proteins were subjected to disease-associated genes and variants screening by DisGeNET. Apart from the diseases that have already been associated with M6a, most of the proteins are also involved in "autistic disorder," "epilepsy," and "seizures" increasing the spectrum of disorders in which M6a could play a role. Data are available via ProteomeXchange with identifier PXD017347.

Neuronal Glycoprotein M6a: An Emerging Molecule in Chemical Synapse Formation and Dysfunction

“…M6a was found within a complex of 30 interacting proteins, some of which are myelin sheath proteins, including the main myelin glycoproteins PLP and MAG; or are myelin sheath associated proteins like contactin 1 and contactin associated protein 1. In agreement, we identified 20 myelin proteins in the co-immunoprecipitation complexes formed by M6a's extracellular domains and rat hippocampal samples, in which PLP was experimentally confirmed (Aparicio et al, 2020). Also, Jahn et al (2020) identified M6a in the myelin sheath of post mortem human brains.…”

“…(C) We hypothesize that M6a function depends on its association with partner proteins in specific membrane microdomains. These associations, induce auto/phosphorylation in specific C-terminal residues facing the cytoplasm, and finally promote neuronal plasticity ( Fuchsova et al, 2009 ; Scorticati et al, 2011 ; Formoso et al, 2015a , b ; Garcia et al, 2017 ; Honda et al, 2017 ; Aparicio et al, 2020 ). For example, M6a can associate with extracellular matrix proteins such as brevican and tenascin C through its extracellular loops in trans and/or with cell adhesion proteins (NCAM and NPTN) through its extracellular domains in cis , triggering its phosphorylation and therefore the recruitment of adapter proteins (such as Rap) and the activation of protein kinases that finally promote the reorganization of the cytoskeleton.…”

“…Recent proteomic studies identified proteins associated with M6a that participate in neurite outgrowth and axon elongation ( Figures 1B,C ; Sato et al, 2011a ; Huttlin et al, 2017 ; Aparicio et al, 2020 ; Haenig et al, 2020 ; Pourhaghighi et al, 2020 ). To emphasize some examples, we divided them into 3 groups: (i) Cytoplasmic proteins: which include cytoskeleton adaptor molecules and cytoskeleton organization pathways which might interact with M6a’s cytoplasmic tails as Ras kinases 2, DiRas2 ( Grunewald et al, 2021 ) and the kinases mentioned above.…”

“…Recently, M6a has also been associated with other SVs and presynaptic active zone—PAZ—residents proteins, like synaptic vesicle protein 2B (SV2B), piccolo, bassoon, and synapsin 1 ( Aparicio et al, 2020 ). Overexpression of M6a in hippocampal neurons showed a significant increment of synaptophysin puncta correlating with an increase in the number of synapses.…”

“…Conversely, M6a was detected in a proteomic analysis of enriched postsynaptic membrane fractions from mice brains, suggesting a postsynaptic localization for M6a ( Reim et al, 2017 ). Besides, we described that M6a co-immunoprecipitated with integral components of the postsynaptic membranes such as metabotropic glutamate receptor 1 (GRM1), voltage-dependent anion channel 1 (VDAC1), and N-methyl-D-aspartate receptor type 1, NMDA-R1 (GR1A1) ( Aparicio et al, 2020 ). Indeed, M6a-overexpressing neurons exhibited an increase in the number of NMDA-R1 clusters, whilst truncated forms of M6a or its depletion decreased the number of NMDA-R1 clusters ( Formoso et al, 2016 ; Garcia et al, 2017 ).…”