Regulation of Myosin-XIX by Non-Muscle Tropomyosins Cameron Parker Thompson

Format:

Book

Thesis/Dissertation

Author/Creator:

Thompson, Cameron Parker, author.

Contributor:

University of Pennsylvania. Biochemistry and Molecular Biophysics., degree granting institution.

Language:

English

Subjects (All):

0307.

0379.

0487.

0786.

Local Subjects:

0307.

0379.

0487.

0786.

Physical Description:

1 electronic resource (119 pages)

Contained In:

Dissertations Abstracts International 87-07B

Place of Publication:

Ann Arbor : ProQuest Dissertations and Theses, 2025

Language Note:

English

Summary:

Mitochondria are highly dynamic organelles that not only act as the primary source of energy in a cell but also function as a hub of signaling and metabolism. To properly play this role in the cell, the mitochondrial network must maintain proper morphology and localization within the cell. Most of this balancing act is driven by the cytoskeletal system, a collection of protein filaments, motors, adaptors, and regulators which helps maintain cellular architecture as well as providing the highways on which cargos are trafficked. In this dissertation, we explore the ways that the mitochondrial myosin, Myosin-XIX, is regulated to promote or inhibit its interaction with the actin cytoskeleton. We decided to focus on the tropomyosin family of proteins, a collection of 40+ protein isoforms resulting from the alternative splicing of four genes which collectively bind and coat actin filaments. These proteins have been shown in the past to have differential regulation of myosin motors; some are inhibited by tropomyosin presence while others are activated. Using purified Myosin-XIX and tropomyosin proteins, we performed in vitro actin gliding assays to determine what role tropomyosins may play in regulating Myosin-XIX. We discovered that Myosin-XIX displays a tropomyosin concentration dependent inhibition. This inhibition behaves in an "all-or-none" manner, below a critical concentration the myosin is able to bind and glide actin filaments. However, when that critical concentration is passed, filaments release from the surface. This suggested a highly cooperative regulatory mechanism in which the motor and tropomyosin likely compete for binding on actin, which was supported by in vitro TIRF microscopy experiments.Within the cell, mitochondria interact with both stable and dynamic actin populations. We were curious if any of these populations of actin filaments also contained tropomyosin. Using immunocytochemistry, we found that mitochondrially-associated actin filaments contain tropomyosin 3, one of the isoforms we found inhibited Myosin-XIX in vitro. We used live-cell imaging to explore the Tpm distribution on dynamic actin populations. We observed the interphase actin wave cycling through the cytoplasm, but we were surprised to also observe a cycling Tpm3.1 wave. Quantitative analysis of the dynamics of the two waves found that the actin wave proceeds the Tpm wave, but the Tpm wave persists for a longer period after the actin wave leaves. Given the ubiquitous presence of Myosin-XIX on the outer mitochondrial membrane, our biochemical discovery of the inhibition of the motor by Tpms combined with the novel cycling Tpm wave represent a mechanism by which the cell can spatiotemporally regulate the motor activity

Notes:

Advisors: Ostap, E. Michael; Holzbaur, Erika L. F. Committee members: Lakadamyali, Melike; Dominguez, Roberto; Chang, Yi-Wei; Yengo, Christopher

Source: Dissertations Abstracts International, Volume: 87-07, Section: B.

Ph.D. University of Pennsylvania 2025

Vendor supplied data

Local Notes:

School code: 0175

ISBN:

9798276004785

Access Restriction:

Restricted for use by site license