Biology subjects

Burghardt, T. P.

Publications and source records attributed to Burghardt, T. P..

3 recordsLinked to original sources

bioRxiv2018

Uncured PDMS Inhibits Myosin In Vitro Motility in a Microfluidic Flow Cell

The myosin motor powers cardiac contraction and is frequently implicated in hereditary heart disease by its mutation. Principal motor function characteristics include myosin unitary step size, duty cycle, and force-velocity relationship for translating actin under load. These characteristics are sometimes measured in vitro with a motility assay detecting fluorescent labeled actin filament gliding velocity over a planar array of surface immobilized myosin. Assay miniaturization in a polydimethylsiloxane/glass (PDMS/glass) hybrid microfluidic flow channel is an essential component to a small sample volume assay applicable to costly protein samples however the PDMS substrate dramatically inhibits myosin motility. Myosin in vitro motility in a PDMS/glass hybrid microfluidic flow cell was tested under a variety of conditions to identify and mitigate the effect of PDMS on myosin. Substantial contamination by the monomeric species in polymerized PDMS flow cells is shown to be the cause of myosin motility inhibition. Normal myosin motility recovers by either extended cell aging ([~]20 days) to allow more complete polymerization or by direct chemical extraction of the free monomers from the polymer substrate. PDMS flow cell aging is the low cost alternative compatible with the other PDMS and glass modifications needed for in vitro myosin motility assaying.

biophysics↗

bioRxiv2018

Cardiac and Skeletal Actin Substrates Uniquely Tune Cardiac Myosin Strain-Dependent Mechanics

Native cardiac ventricular myosin ({beta}mys) translates actin under load by transducing ATP free energy into mechanical work on actin during muscle contraction. Unitary {beta}mys translation of actin is the myosin step-size. In vitro and in vivo {beta}mys regulates contractile force and velocity by remixing 3 different step-sizes with stepping frequencies autonomously adapted to workload. Cardiac and skeletal actin isoforms have a specific 1:4 stoichiometry in normal adult human ventriculum. Human adults with inheritable hypertrophic cardiomyopathy (HCM) up-regulate skeletal actin in ventriculum suggesting that increasing skeletal/cardiac actin stoichiometry also adapts myosin force-velocity to respond to the muscles inability to meet demand.\n\nNanometer scale displacement of quantum dot (Qdot) labeled actin under resistive load when impelled by {beta}mys measures single myosin force-velocity in vitro in the Qdot assay. Unitary displacement classification constraints introduced here better separates myosin based signal from background upgrading step-size spatial resolution to the sub-nanometer range. Single {beta}mys force-velocity for skeletal vs cardiac actin substrates was compared using the Qdot assay.\n\nTwo competing myosin strain-sensitive mechanisms regulate step-size choices dividing mechanical characteristics into low- and high-force regimes. The actin isoforms alter myosin strain-sensitive regulation such that onset of the high-force regime, where a short step-size is a large or major contributor, is offset to higher loads by a unique cardiac ELC N-terminus/cardiac-actin contact at Glu6/Ser358. It modifies {beta}mys force-velocity by stabilizing the ELC N-terminus/cardiac-actin association. Uneven onset of the high-force regime for skeletal vs cardiac actin dynamically changes force-velocity characteristics as skeletal/cardiac actin fractional content increases in diseased muscle.

biophysics↗

bioRxiv2017

Single Cardiac Ventricular Myosins Change Step-Size with Loading

The cardiac myosin motor powers the beating heart by catalyzed ATPase free energy conversion to contractile work. Transgenic mouse models for heart disease express mouse -cardiac myosin heavy chain with human essential light chain (ELC) in wild type (WT), or hypertrophic cardiomyopathy linked mutant forms, A57G or E143K. Mutants modify the ELC actin binding N-terminus or C-terminus regions. Motility and single myosin mechanical characteristics show stark contrasts between the motors related to their average force, power, and displacement while all indicate the ability to down-shift ensemble step-size with increasing load. A57G and E143K consume more ATP than control WT in the presence of actin with A57G upregulating and E143K downregulating power compared with WT. Higher ATP consumption and downregulated power in E143K implies a lower unitary force. Effects on power are consistent with an A57G that impairs the ELC N-terminus actin binding and an E143K that reduces lever-arm rigidity.

biophysics↗