Abstracts Category : Other

Molecular interactions of AMIGO family members in the Nogo receptor complex

by Rachael Hannah Bennett

The capacity for regeneration in the central nervous system is limited, with little functional recovery following injury or disease. Upon injury, the CNS responds by releasing myelin associated inhibitory factors (MAIFs), including Nogo, MAG and OMgp, which act to suppress axonal regrowth by binding to the Nogo receptor (NgR) complex. The complex consists of the Nogo receptor (NgR), p75 neurotrophin receptor (p75NTR), (or an alternative protein, TROY) and LINGO-1. Signalling through the complex leads to activation of RhoA, resulting in growth cone collapse. However, the specific mechanisms by which the complex exhibits its effects remain unclear, particularly as more recent data suggest that specific members of the AMIGO family of proteins may be critical mediators of the inhibitory signaling pathway. Mammalian expression and subcellular fractionation and co-immunoprecipitation experiments established binding between both NgR and p75NTR with AMIGO-1, -2 and -3 and have shown the AMIGO proteins are expressed in the cell membrane as are NgR and p75NTR. Interestingly LINGO-1 was also shown to be expressed intracellularly. Furthermore, injection of soluble LINGO-1, AMIGO-1 and AMIGO-3 in surface plasmon resonance (SPR) approaches confirmed interaction with surface bound NgR. Finally, the structure of the human AMIGO-1 ectodomain, including LRR and Ig domains was determined to 1.9 resolution. The protein formed a dimer in solution and crystal form and comparisons with structurally similar LRR and Ig domain containing proteins, combined with electrostatic properties and localisation of glycosylation sites, was used to ascertain likely ligand binding sites on the surface of the protein and AMIGO family in general. Collectively these results indicate that the AMIGO proteins may form a component of the axon growth inhibitory complex, and are potentially novel therapeutic targets for CNS injury.