Research

Protein-Protein Interactions in the Extracellular Milieu

Structural biology of Synaptic and Axonal Complexes

Protein-Protein Interactions in the Extracellular Milieu

Cell surface protein-protein interactions encode for connectivity between cells in multicellular organisms. We are working on revealing the set of interactions that build animals, and especially the nervous system. We focus on invertebrate systems, mostly for their simplicity – fewer cell surface receptors and neurons/neuronal classes – and based on an assumption that activity-dependent wiring mechanisms are less prevalent.

Our first pass of the fruit fly extracellular interactome has already yielded sets of interactions that direct synaptic specificity, retrograde signaling at the synapse, neuronal survival and axon guidance.

Reference: An extracellular interactome of immunoglobulin and LRR proteins reveals receptor-ligand networks. Özkan E, Carrillo RA, Eastman CL, Weiszmann R, Waghray D, Johnson KG, Zinn K, Celniker SE, Garcia KC. Cell 154, 228 (2013).

Reference: Control of synaptic connectivity by an interacting network of Drosophila IgSF cell surface proteins. Carrillo RA*, Özkan E*^§, Menon K*, Nagarkar-Jaiswal S, Lee PT, Jeon M, Birnbaum ME, Bellen HJ, Garcia KC, Zinn K^§. Cell 163, 1770 (2015). (* equal contribution, ^§ corresponding authors)

Reference: Deconstruction of the Beaten Path-Sidestep interaction network provides insights into neuromuscular system development. Li H, Watson A, Olechwier A, Anaya M, Sorooshyari SK, Harnett DP, Lee HKP, Vielmetter J, Fares MA, Garcia KC, Özkan E, Labrador JP, Zinn K. Elife 6, e28111 (2017).

Reference: Molecular basis of synaptic specificity by immunoglobulin superfamily receptors in Drosophila. Cheng S, Ashley J, Kurleto JD, Lobb-Rabe M, Park YJ, Carrillo RA, Özkan E. Elife 8, e41028 (2019).

Structural Biology of Synaptic and Axonal Complexes

Cell surface receptors are our accessible handles to controlling cell function and fate, without having to cross cell membranes. We are discovering and characterizing interactions of cell surface receptors with secreted or cell-surface ligands to have insights into several developmental processes in the nervous system, such as synapse formation, axon guidance, neuronal growth and regeneration.

We are currently studying several neuronal and glial receptors that guide exons and control synapse formation, which were discovered or detected in our high-throughput screens for cell surface protein interactions.

Left: Neurexin-Cerebellin-GluD2 complex at the Granule cell-Purkinje cell synaptic cleft (Cheng et al., Structure 2016). Right: Immunoglobulin Superfamily Cell Adhesion Complexes (Cheng et al., PNAS 2019).

Our method of choice for a molecular understanding of protein-protein interactions is X-ray crystallography. We supplement it with electron microscopy and other biophysical methods, while we work with model organism geneticists and neuroscientists to test biochemical and mechanistic hypotheses in vivo.

Reference: Extracellular Architecture of the SYG-1/SYG-2 Adhesion Complex Instructs Synaptogenesis. Özkan E, Chia PH, Wang RR, Goriatcheva N, Borek D, Otwinowski Z, Walz T, Shen K, Garcia KC. Cell 156, 482 (2014).

Reference: Conformational Plasticity in the Transsynaptic Neurexin-Cerebellin-Glutamate Receptor Adhesion Complex. Cheng S, Seven AB, Wang J, Skiniotis G, Özkan E. Structure 24, 2163 (2016).

Link