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Topic

Toward an understanding of agonistic antibody fragments binding to TrkB

Department of Biochemistry and Microbiology

Date & location

• Thursday, March 19, 2026

• 3:00 P.M.

• Engineering & Computer Science Building

• Room 128

Reviewers

Supervisory Committee

• Dr. Stephen Evans, Department of Biochemistry and Microbiology, ̽��ϵ�� (Supervisor)

• Dr. Alisdair Boraston, Department of Biochemistry and Microbiology, UVic (Member)

• Dr. John Taylor, Department of Biology, UVic (Outside Member) 

External Examiner

• Dr. Douglas Briant, Department of Biochemistry and Microbiology, UVic 

Chair of Oral Examination

• Dr. Ian Putnam, Department of Mathematics and Statistics, UVic

   

Abstract

Tropomyosin receptor kinase B (TrkB) activation plays important roles in neuronal development and synaptic plasticity, as well as in disease states such as Alzheimer’s (AD). Published studies in mouse models revealed the therapeutic potential of agonistic anti-TrkB antigen binding fragments of antibodies (Fabs) to alleviate AD symptoms. The precise epitopes of these Fabs and the molecular basis of their associated activation mechanisms have not yet been determined. Gaining an understanding of these TrkB-Fab interactions will be valuable to the development of novel AD treatment. In this study, three subdomains of TrkB were successfully expressed individually as soluble proteins and purified. SPR analysis with collaborators verified that these TrkB subdomains bind to selected agonistic anti-TrkB Fabs, indicating that the assignment of specificity of antibody to subdomain was correct. Attempts to crystallize the TrkB subdomains alone and with their corresponding Fabs have not been successful. However, crystals measuring at least 0.1 mm on each side of two of the Fabs individually were produced but none diffracted beyond ~4 Å resolution, making them unsuitable for detailed structural determination. To provide insight as to why these Fabs were difficult to crystallize and to give further evidence that the Fabs themselves were correctly folded, a 4.5 Å resolution data set collected previously for one of the Fabs was solved. The structure showed rough electron density that corresponded to the path of the main chain atoms, which confirmed that the variable and constant domains of both Fabs in the asymmetric unit displayed the expected immunoglobulin folds; however, most of the longer complementarity-determining regions (CDRs) did not show convincing electron density. A comparison of the CDR lengths revealed that some were longer than average for murine κ antibodies. The expected flexibility of these longer CDR loops may have contributed to the difficulties encountered with crystallization.