Y. Ava Lin

     Email: linxx318@umn.edu

     Year Entered: 2006

     Degrees Received:
     University of California, Irvine
     Molecular Biology and Biochemistry major
     B.S., 2006

     University of Minnesota
     Biochemistry, Molecular Biology and Biophysics Graduate
     Ph.D., 2012

     Honors and Awards:

     -NIH/NIA National Research Service Award for Individual
     Predoctoral MD/PhD Fellows, 2009-2014
     -Minnesota Medical Foundation Milne-Brandenburg Award, 2012

Thesis Advisor: David Thomas, Ph.D.

Thesis Research: Structural dynamics of the actin-binding domains in dystrophin and utrophin

Dystrophin and utrophin bind actin in vitro with similar affinities, but with different molecular contacts (Rybakova et al, 2006, J. Biol. Chem). It is proposed that these differences alter the elasticity of dystrophin-actin and utrophin-actin linkages to the sarcolemma, affecting the cell's response to muscle stretches. To test this hypothesis, we have determined the effects of dystrophin and utrophin on the microsecond dynamics of phosphoresescent-labeled actin, using transient phosphorescence anisotropy (TPA). At higher levels of saturation, utrophin was more effective than dystrophin in causing changes to the final anisotropy, correlation time, and initial anisotropy of actin dynamics. The simplest interpretation of these changes is that utrophin restricted the amplitude and increased the rates of actin to a substantially larger extent than dystrophin. Further analysis indicated that the actin-utrophin complex is much more torsionally flexible than the actin-dystrophin complex. We propose that these differences between dystrophin and utrophin in their effects on actin dynamics affect elastic properties of actin-mediated linkages with the sarcolemma. (Prochniewicz et al., 2009, PNAS) Preliminary data on fragments containing all the proposed actin binding domains (DN-R17/UN-R10) show less of an effect on regulating rotational amplitude and nearly no effect on rotational rate. Future experiments looking at other fragments of dystrophin and utrophin, and constructs with engineered disease-causing point mutations will determine which structural elements of these proteins are critical in determining the flexibility of actin filaments and what level of actin flexibility is physiologically optimal. Finally, to test the hypothesis that different orientation or conformation of the actin binding domain in dystrophin and utrophin contributes to changes in actin dynamics, we are using spectroscopic probes to do direct distance measurements between the 2 Calponin homology actin-binding domain heads to differentiate between the 4 currently proposed models of CH domains conformation in utrophin N-terminal actin-binding domain (Lin et al., 2010, PNAS). Analogous studies are underway to study the CH domains in dystrophin.

Publications (pubmed):

Lin AY, Prochniewicz E, Henderson DM, Li B, Ervasti JM, Thomas DD. Impacts of dystrophin and utrophin domains on actin structural dynamics: implications for therapeutic design. J Mol Biol. 2012 Jun 29;420(1-2):87-98.

Henderson DM, Lin AY, Thomas DD, Ervasti JM. The carboxy-terminal third of dystrophin enhances actin binding activity. J Mol Biol. 2012 Feb 24;416(3):414-24.

Lin AY, Prochniewicz E, James ZM, Svensson B, Thomas DD. Large-scale opening of utrophin's tandem calponin homology (CH) domains upon actin binding by an induced-fit mechanism. Proc Natl Acad Sci U S A. 2011 Aug 2;108(31):12729-33.