Date of Degree

9-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Jayne Raper

Committee Members

Paul Feinstein

Mitchell Goldfarb

Nina Papavasiliou

Michael Steiper

Subject Categories

Biochemistry | Evolution | Immunity | Molecular Biology | Parasitology

Keywords

Trypanosoma brucei, innate immunity, primate evolution, genetic engineering

Abstract

Trypanosome lytic factors (TLFs) are primate-specific antimicrobial protein complexes that lyse African trypanosome parasites by delivering the channel-forming toxin APOL1 to the invading microorganisms. Human serum contains two TLFs that are delivered to the parasite by separate mechanisms, only one of which has been characterized. TLF1 is endocytosed by a receptor that is typically blocked by other serum factors in vivo, suggesting that TLF2 is the more relevant lytic factor in the context of trypanosome immunity. TLF2 is non-covalently associated with polyclonal immunoglobulin M (IgM) antibodies, which we report here to be involved in the uptake mechanism. The TLF2-IgMs are polyreactive and can interact with both the TLF complex and the dominant surface protein of trypanosomes, the variant surface glycoprotein (VSG), which likely drives uptake of the APOL1. Once delivered to the parasite, human APOL1 forms cation selective pH-gated channels in membranes. However, relatively little is known about the channel forming properties of non-human primate APOL1 proteins or their TLF complexes. Here we also report that non-human primates, including the baboon, have both TLF1 and TLF2 complexes. We have investigated the channel forming properties of baboon APOL1 and have observed that it is less restricted by pH than human APOL1, which we have attributed to key amino acid differences between the two proteins. In order to better understand the function of human and primate TLFs, we have generated various mouse models allowing us to study them in vivo, including an array of targeted germline transgenic baboon APOL1-expressing animals. These mice have been used to model the possibility of creating genetically modified livestock with a similar strategy in order to potentially provide a novel method to limit the devastating agricultural burden imposed by trypanosomes on sub-Saharan Africa.

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