Biomechanics of cardiac and skeletal muscle; BioNanotechnology

General research areas: Biophysics of muscle tissue, molecular motor proteins, and calcium regulation of contraction; cellular and molecular biomechanics of cardiac and skeletal muscle; BioNanotechnology.

Research tools: Cellular and molecular biomechanical assays of permeabilized cardiac and skeletal muscle; in vitro motility assays; molecular biology; bi oinformatics; biochemical and biomechanical modeling.

Major ongoing projects: Functional consequences of mutations in troponin I that cause hypertrophic cardiomyopathy; molecular and cellular biochemical/bio mechanical model of striated muscle\x97a component of NASA/NSBRI\x92s "digital human." Inquire about additional projects.

The central theme of my research program is to understand the biophysical basis of biological motility, its regulation, and its modulation by cellular metabolis m. Much remains to be learned about actomyosin interactions and their regulation, especially in cardiovascular function and diseases, cancer (metastasis), huma n performance, and bionanotechnology (biological nanomotors and protein mechanics). My experimental work has most often been directed toward answering molecula r and cellular questions related to these topics; future experimental directions are, at one end of the spectrum, integrative studies using intact animals and, at the other, investigations at the single molecule level.

Troponin I and cardiac hypertrophy: In terms of clinical significance, the most important application\x97and currently my main focus\x97is understanding specific forms of cardiovascular disease, particularly the inherited (familial) forms of hypertrophic cardiomyopathy (FHC) and idiopathic dilated cardiomyopathy (IDC). In the first stage of the project, mutant forms of cardiac troponin I or troponin T are expressed in E. coli for incorporation into molecular and cellular assays that will test for changes in biomechanical function relative to wild type proteins. In its simplest terms, the hypothesis we are testing is whether the mutations cause hypertrophy by inhibiting function (causing compensatory hypertrophy) or by enhanc ing function (causing exercise-like hypertrophy). In later stages of the project, we will test whether mutants affect cardiac-specific modulations: sarcomere l ength (Starling\x92s law) and protein phosphorylation associated with adrenergic stimulation. See Chase et al. (2001) Biophys. J. 80:342a. These studie s complement our previous work on troponin C, the calmodulin-like, Ca²⁺-binding subunit of troponin.

Metabolites, fatigue, and ischemia (intracellular environment): A long-standing problem I have worked on is the cellular basis for contractile deficit in fatigue or ischemia. We use permeabilized cellular preparations\x97in which we directly control metabolite concentrations (e.g., of ATP, ADP, Pi, [H⁺], and others)\x97to study the effects of altered metabolite levels on contractility. Related investigations use structural analogs of inorganic phosphate, aluminum fluoride, and beryllium fluoride. These analogs are interesting for biomechanical studies not only because they permit investigation of Pi in force generation but also for evaluation the physiological relevance of crystallographic structures of myosin motor domain complexes containing these analogs \x97structures considered central to our understanding of how molecular motors work. Other recent studies involve deoxy-ATP as a substrate for actomyosin. The biomechanical response to changes in metabolite concentration depends on the protein isoform(s) being studied (different proteins from different genes or from alternative splicing of mRNA) and could be altered by FHC-related mutations in cTnI (see above).

Modeling: A third research area is molecular and cellular biochemical and biomechanical modeling. Our Monte-Carlo modeling suggests that biomechanical " tuning" arises from finite stiffness of the proteins, and that this property contributes to apparent cooperativity of force generation in the steady-state, isom etric situation. This tuning, observed under load-bearing conditions, will probably be an important design consideration for nanomechanical systems. Future di rections for this project include expanding the model to handle larger ensembles of molecules and developing the tools necessary to test the model predictions.

Chase Lab (Fall '02): Nicolas Brunet, Johnny Hutchinson, Janina Bhuvasorakul, Lisa Compton, Will Chase, Amanda Clark, Fang Wang, Shanedah Williams, Ivan Porter, Lori McFadden, Alyson Barnes. Missing from photo Justin Grubich, Bert Coslow, Vic Miller.

Bio-Nanotechnology @ FSU An interdisciplinary collaboration between Physics/MARTECH, Biological Science, and Chemistry & Biochemistry. P rojects funded through NSF's Nanoscale Science and Engineering Program and DARPA's Biomolecular Motors Program.

Shanedah Williams, Janina Bhuvasorakul, Justin Grubich, Alyson Barnes,
Nicolas Brunet, Fang Wang

Top row: Nicolas Brunet, Stephen Kornbluth, Amanda Clark, Lori McFadden 
Bottom row: Bert Coslow, Alyson Barnes, Shanedah Williams, Justin Grubich