University of Illinois Urbana-Champaign

Single-molecule studies of unconventional motor protein myosin VI

Kim, HyeongJun

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Kim_HyeongJun.pdf

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https://hdl.handle.net/2142/24436

Description

Title
Single-molecule studies of unconventional motor protein myosin VI
Author(s)
Kim, HyeongJun
Issue Date
2011-05-25T14:39:08Z
Director of Research (if dissertation) or Advisor (if thesis)
Selvin, Paul R.
Doctoral Committee Chair(s)
Chemla, Yann R.
Committee Member(s)
  • Selvin, Paul R.
  • Oono, Yoshitsugu
  • Lev, Benjamin L.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Date of Ingest
2011-05-25T14:39:08Z
Keyword(s)
  • Myosin VI
  • Medial tail
  • proximal tail
  • three-helix bundle unfolding
  • single-molecule
Abstract
Myosin VI is one of the myosin superfamily members that are actin-based molecular motors. It has received special attention due to its distinct features as compared to other myosins, such as its opposite directionality and a much larger step size than expected given the length of its “leg”. This dissertation presents the author‟s graduate work of several single-molecule studies on myosin VI. Special attention was paid to some of myosin VI‟s tail domains that consist of proximal tail (PT), medial tail (MT), distal tail (DT) domains and cargo-binding domain (CBD). The functional form of myosin VI in cells is still under debate. Although full length myosin VI proteins in cytosolic extracts of cells were monomers from earlier studies, there are several reasons why it is now believed that myosin VI could exist as a dimer. If this is true and dimerization occurs, the next logical question would be which parts of myosin VI are dimerization regions? One model claimed that the CBD is the sole dimerization region. A competing model claimed that there must be another region that could be involved in dimerization, based on their observation that a construct without the CBD could still dimerize. Our single-molecule experiment with progressively truncated myosin VI constructs showed that the MT domain is a dimerization region, supporting the latter model. Additional single-molecule experiments and molecular dynamics (MD) simulation done with our collaborators suggest that electrostatic salt bridges formed between positive and negative amino acid residues are mainly responsible for the MT domain dimerization. After resolving this, we are left with another important question which is how myosin VI can take such a large step. Recent crystal structure showed that one of the tail domains preceding the MT domain, called the PT domain, is a three-helix bundle. The most easily conceivable way might be an unfolding of the three-helix bundle upon dimerization, allowing the protein to stretch and reach a larger distance. The single-molecule stepping data with mutant full-length construct that lacks two helices out of three in the PT domain tell that it is indeed the case. In this dissertation, more details of myosin VI PT/MT domain experiments will be explored along with background information on the single-molecule experiment methods used in these studies.
Graduation Semester
2011-05
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http://hdl.handle.net/2142/24436
Copyright and License Information
Copyright 2011 HyeongJun Kim

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