Members of the vertebrate contactin and amyloid precursor protein families interact through a conserved interface

Sebastian J Karuppan,Alex Vogt,Zachary Fischer,Aliona Ladutska,Jonathan Swiastyn,Hillary F Mcgraw,Samuel Bouyain

doi:10.1016/j.jbc.2021.101541

Sebastian J Karuppan, Alex Vogt + Show 5 more

Open Access

https://doi.org/10.1016/j.jbc.2021.101541

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Abstract

Contactins (CNTNs) are neural cell adhesion molecules that encode axon-target specificity during the patterning of the vertebrate visual and olfactory systems. Because CNTNs are tethered to the plasma membrane by a glycosylphosphatidylinositol anchor, they lack an intracellular region to communicate across the membrane. Instead, they form coreceptor complexes with distinct transmembrane proteins to transmit signals inside the cell. In particular, a complex of CNTN4 and amyloid precursor protein (APP) is known to guide the assembly of specific circuits in the visual system. Here, using in situ hybridization in zebrafish embryos, we show that CNTN4, CNTN5, and the APP homologs, amyloid beta precursor like protein 1 and amyloid beta precursor like protein 2, are expressed in olfactory pits, suggesting that these receptors may also function together in the organization of olfactory tissues. Furthermore, we use biochemical and structural approaches to characterize interactions between members of these two receptor families. In particular, APP and amyloid beta precursor like protein 1 interact with CNTN3–5, whereas amyloid beta precursor like protein 2 only binds to CNTN4 and CNTN5. Finally, structural analyses of five CNTN–amyloid pairs indicate that these proteins interact through a conserved interface involving the second fibronectin type III repeat of CNTNs and the copper-binding domain of amyloid proteins. Overall, this work sets the stage for analyzing CNTN–amyloid-mediated connectivity in vertebrate sensory circuits.

Highlights

Trillions of synaptic connections are established with exquisite specificity during the patterning of the vertebrate nervous system
Because amyloid precursor protein (APP) and its homologs, amyloid beta precursor like protein 1 (APLP1) and amyloid beta precursor like protein 2 (APLP2), have broadly overlapping functions [8] and because both APP and APLP1 interact with CNTN3–5 [9, 10], we hypothesized that coreceptor complexes formed by APPs and CNTNs could participate in the array of adhesive interactions that ensure appropriate targeting of axons and dendrites in neural sensory circuits
We thought that zebrafish was an ideal organism to carry out this work because (i) the anatomy of the zebrafish nervous system closely resembles the human one [11], (ii) pathways underlying the development of the nervous system are broadly conserved between zebrafish and humans [12, 13], (iii) 70% of human genes, including app, aplp1, aplp2, and cntn1–5, have clear orthologs in fish [14], and (iv) embryos are translucent and accessible

Summary

Introduction

Trillions of synaptic connections are established with exquisite specificity during the patterning of the vertebrate nervous system. These differences in binding affinities indicate that CNTN4 may be the preferred binding partner for APP among CNTNs. We repeated these experiments using the E1 domain human APLP1 versus the FN1–FN3 regions of CNTN3–5 (Fig. 3B).

Results

Conclusion