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The H. polygyrus TGF-β Mimic TGM6: A Competitive Inhibitor of TGF-β Signaling

White, Stephen Evans (2023) The H. polygyrus TGF-β Mimic TGM6: A Competitive Inhibitor of TGF-β Signaling. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The murine helminth parasite Heligmosomoides polygyrus expresses a family of structurally novel mimics of TGF-β, first identified through TGF-β Mimic 1 (TGM1), a 5-domain protein which binds and signals through the TGF-β receptors, TβRI and TβRII. Through recent studies, domains 1 and 2 and domain 3 have been shown to bind TβRI and TβRII, respectively. The function of domains 4 and 5 remain undefined. TGM6 is a homologue of TGM1 in which domains 1 and 2 are absent. In this work, biophysical methods and cellular assays were used to characterize its specificity, structure, and function. In accord with TGM1, TGM6 is shown to bind TβRII through domain 3. However, TGM6 does not bind the TGF- family type I receptors Alk1, Alk2, Alk3, Alk4, or Alk5 or type II receptors ActRII, ActRIIb, or BMPRII. In cellular TGF-β reporter assays, TGM6 is shown to act as a highly potent TGF-β and TGM-1 signaling antagonist, consistent with its ability to bind TβRII, but not other receptors of the TGF-β family previously stated. TGM6, however, inhibits TGF-β signaling in mouse fibroblast cell lines and only does so when domains 4 and 5 are present, suggesting that domains 4, 5, or 4 and 5 are bound by a co-receptor that potentiates the inhibitory activity of TGM6. To gain insights as to how TGM6 specifically binds TβRII, the X-ray crystal structure of the TGM6-D3 bound to TβRII was determined to 1.45 Å. This shows that TGM6-D3 binds TβRII through an interface that is remarkably similar to that of TGF-β:TβRII. These results, together with the finding that TGM6 binds TβRII with high affinity, suggest that TGM6 has specifically adapted its domain structure and sequence to function as a potent TGF-β and TGM antagonist, possibly to blunt fibrotic damage caused by the parasite as it progresses through its life cycle.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
White, Stephen Evansstw59@pitt.edustw590000-0002-7786-4400
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairIshima, Riekoishima@pitt.eduishima
Thesis AdvisorHinck, Andrew P.ahinck@pitt.eduahinck
Committee MemberRule,
Vignali, Dariodvignali@pitt.edudvignali
Date: 15 September 2023
Date Type: Publication
Defense Date: 13 June 2022
Approval Date: 15 September 2023
Submission Date: 6 August 2022
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 249
Institution: University of Pittsburgh
Schools and Programs: School of Medicine > Molecular Biophysics and Structural Biology
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: TGF-, H. polygyrus, parasite, Hp-TGM, TGM6, NMR, X-ray crystallography, biophysics, structural biology, protein structure, isothermal titration calorimetry, ITC, surface plasmon resonance, SPR, reporter assay
Date Deposited: 15 Sep 2023 15:28
Last Modified: 15 Sep 2023 15:28


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