Dr. Robert W. Kensler

RCM A-502
787-758-2525, x1507

Interests: Macromolecular structures of the muscular gross fibers.

In my laboratory, the primary research objective is to elucidate the structure of the myosin-containing thick filaments found in striated muscles. The goal of the work is to understand how differences in the packing of myosin and accessory proteins in thick filaments from different muscles may relate to differences in the physiological properties of the muscles and to understand the mechanism of force production at the molecular level. The key principle guiding much of the work is the observation from X-ray diffraction studies that the heads of the myosin molecules on the filament in living muscle are helically arranged. We have been one of the pioneering laboratories in the development of procedures which allow filaments from some muscles to be biochemically isolated with the helical arrangements of heads largely preserves, thus making the structure of the filaments amenable to analysis by a combination of electron microscopy with computer image analysis of the electron micrographs. This approach utilizes the principles of helical diffraction and computer image analysis of helical structures to determine the helical parameters and to compute a three-dimensional reconstruction of the electro density of the proteins in the thick filament.

Using this approach we have computed three-dimensional reconstructions both of several invertebrate (horseshoe crab and scorpion) and vertebrate (frog and fish) skeletal muscle thick filaments. The primary goal of the current research is to elucidate the structure of the mammalian cardiac muscle thick filament; and to study the effects of phosphorylation of myosin light chain and other thick filaments accessory proteins on the structure of the thick filaments and their interactions with actin to produce contraction. Determination of the structure of the cardiac thick filament as compared to the skeletal muscle thick filament is important for understanding the differences in physiological properties of cardiac muscle and skeletal muscle.

The techniques employed in the laboratory include electron microscopy (negative staining and platinum shadowing), computer image analysis both Fourier analysis and single particle analysis, cell fractionation, centrifugation, and SDS gel electrophoresis. Training opportunities are available for graduate students, undergraduates, and medical students.

Present Funding: NIH MBRS, American Heart Association

Selected Publications:

  • Kensler, R.W., R. Craig, and R.L. Moss. Phosphorylation of cardiac myosin binding protein C releases myosin heads from the surface of cardiac thick filaments. Proc Natl Acad Sci USA. 114(8):E1355-E1364. 2017.
  • Mun JY, R.W. Kensler, S.P. Harris, and R. Craig. The cMyBP-C HCM variant L348P enhances thin filament activation through an increased shift in tropomyosin position. J Mol Cell Cardiol. 2016 Feb;91:141-7. 2016.
  • González-Solá M*, Al-Khayat HA, Behra M, Kensler RW (2014) Zebrafish cardiac muscle thick filaments: isolation technique and three-dimensional structure. Biophys J. 106(8):1671-80.
  • Al-Khayat HA, Kensler RW, Squire JM, Marston SB, Morris EP (2013) Atomic model of the human cardiac muscle myosin filament. Proc Natl Acad Sci U S A. 110(1):318-23.
  • Kensler RW, Shaffer JF, Harris SP (2011) Binding of the N-terminal fragment C0-C2 of cardiac MyBP-C to cardiac F-actin. J Struct Biol 174(1):44-51.
  • Al-Khayat HA, Kensler RW, Morris EP, Squire JM (2010) Three-dimensional structure of the M-region (bare zone) of vertebrate striated muscle myosin filaments by single-particle analysis. J Mol Biol 403(5):763-776.
  • Paul DM, Morris EP, Kensler RW, Squire JM. (2009) Structure and orientation of troponin in the thin filament. J Biol Chem. 284:15007-15.
  • Shaffer JF, Kensler RW, Harris SP. (2009) The myosin-binding protein C motif binds to F-actin in a phosphorylation-sensitive manner. J Biol Chem. 284:12318-27.
  • Al-Khayat, H., E. P. Morris, R. W. Kensler, and J. M. Squire (2008) Myosin Filament 3D Structure in Mammalian Cardiac Muscle. J. Structural Biol. 163:117-126.
  • Kensler RW, SP Harris. (2007) The Structure of Isolated Myosin Thick filaments from cMyBP-C Knockout Mice. Biophys J, 94:1707-1718.
  • Al-Khayat H, EP Morris, RW Kensler, JM Squire. (2006) 3D Structure of Relaxed Fish Muscle Myosin Filaments by Single Particle Analysis. J Structural Biol, 155:202-217.
  • Kensler RW. (2005) The Mammalian Cardiac Muscle Thick Filament: Crossbridge Arrangement. J Structural Biol, 149:303-312.
  • Kensler RW. (2005) The Mammalian Cardiac Muscle Thick Filament: Backbone Contributions to Meridional Reflections. J Structural Biol, 149:313-324.
  • Kensler RW. (2002) Mammalian Cardiac Muscle Thick Filaments: Their Periodicity and Interactions with Actin Biophys J, 82:1497.
  • Levine RJC, RW Kensler. (2002) The Thick Filament of Vertebrate Striated Muscle: The Structure at Rest and at Work. In: Cardiovascular Regulation (Ed. R. Moss and J. Solaro). Kluwer Press.
  • Eakins F, HA Al-Khayat, RW Kensler, EP Morris, JM Squire. (2002) 3D-Structure of Fish Muscle Myosin Filaments. J Structural Biol, 137:154-163.
  • Levine RJC, Kensler RW, A Kensler, Z Yang, JT Stull, HL Sweeney. (1996) Myosin Light Chain Phosphorylation Affects the Structure of Rabbit Skeletal Muscle Thick Filaments. Biophysical J. 71:898-907.
  • Kensler RW, JL Woodhead. (1995) The Chicken Muscle Thick Filament: Temperature and the Relaxed Crossbridge Arrangement. J Muscle Res Cell Motil. 16:79-90.
  • Levine RJC, Kensler RW, Z Yang, HL Sweeney. (1995) Myosin Regulatory Light Chain Phosphorylation and the Production of Functionally Significant Changes in Myosin Head Arrangement on Striated MuscleTthick Filaments. Biophysical J. 68:224s.
  • Kensler RW, S Peterson, M Norberg. (1994) The Effects of Changes in Temperature or Ionic Strength on Isolated Rabbit and Fish Thick Filaments. J Muscle Research & Cell Motility 15:69-79.
  • Kensler RW, M Stewart. (1993) The Relaxed Crossbridge Pattern in Isolated Rabbit Psoas Muscle Thick Filaments. J Cell Sci, 105:841-848.
  • Levine RJC, PD Chantler, RW Kensler, J Woodhead. (1991) The Effects of Phosphorylation by Myosin Light Chain Kinase on the Structure of Limulus Thick Filaments. J Cell Biol. 113:563-57.
  • Levine RJC, S Davidheiser, AM Kelly, RW Kensler, J Leferovich, RE Davies. (1989) Fibre Types in Limulus Telson Muscles: Morphology and Histochemistry. J Muscle Research and Cell Motility 10:53-56.
  • Chantler PD, RW Kensler. (1989) Position of Mercenaria Regulatory Light-chain Cys 50 Site on the Surface of Myosin Visualized by Electron Microscopy. J Mol Biology 207:631-636.
  • Kensler RW, M Stewart. (1989) An Ultrastructural Study of Crossbridge Arrangement in the Fish Skeletal Muscle Thick Filament. J Cell Sci. 94:391-401.
  • Levine RJC, PD Chantler, RW Kensler. (1988) Arrangement of Myosin Heads on Limulus Thick Filaments. J Cell Biology 107:1739-1747.
  • Kensler RW, M Stewart (1986) An Ultrastructural Study of Crossbridge Arrangement in the Frog Thigh Muscle Thick Filament. Biophys J. 49:343-351.
  • Levine RJC, RW Kensler, P Levitt (1986) Crossbridge and Backbone Structure of Invertebrate Thick Filaments. Biophys J. 49:136-138.
  • Stewart M, RW Kensler. (1986) Arrangement of Heads in Relaxed Thick Filaments from Frog Skeletal Muscle. J Mol Biol. 192:831-851.
  • Levine RJC, RW Kensler. (1985) Structure of Short Thick Filaments from Limulus Muscle. J Mol Biol 182:347-352.
  • Kensler RW, RJC Levine, M Stewart. (1985) Electron Microscopic and Optical Diffraction Analysis of the Structure of Scorpion Muscle Thick Filaments. J Cell Biol. 101:395-401.
  • Stewart M, RW Kensler, RJC Levine (1985) Three-Dimensional Reconstruction of Thick Filaments from Limulus and Scorpion Muscle. J Cell Biol 101:402-411.
  • Levine RJC, RW Kensler, W Hofmann, S Davidheiser, RE Davies. (1984) Structure of Limulus and Other Invertebrate Thick Filaments. In: Crossbridge Mechanisms in Muscle Contraction. GH Pollock & H Sugi (eds.), Plenum Press, N.Y., pp. 93-106.
  • Kensler RW, M Stewart. (1983) Frog Skeletal Muscle Thick Filaments are Three Stranded. J. Cell Biol. 96:1797-1802.
  • Levine RJC, RW Kensler, MC Reedy, W Hofmann, HA King (1983) Structure and Paramyosin Content of Tarantula Thick Filaments. J Cell Biol. 97:186-195.
  • Kensler RW, RJC Levine. (1982) Determination of the Handedness of the CrossBridge Helix of Limulus Thick Filaments. J Muscle Res and Cell Motil. 3:349-361.
  • Kensler RW, RJC Levine (1981) An Electron Microscopic and Optical Diffraction Analysis of the Structure of Limulus Telson Muscle Thick Filaments. J Cell Biol. 92:443-451.
  • Stewart M, RW Kensler, RJC Levine. (1981) The Structure of Limulus Telson Muscle Thick Filaments. J Mol Biol. 153:781-790.
  • Levine RJC, RW Kensler, M Stewart, JC Haselgrove. (1981) The Molecular Organization of Limulus Thick Filaments. In: Basic Biology of Muscle: A Comparative Approach. B. Twarog, R.J.C. Levine and M.M. Dewey (eds.), Raven Press, N.Y., pp. 37-52.
  • Brink P, MM Dewey, D Colflesh, RW Kensler. (1981) Polymorphic Nexuses in the Earthworm Lumbricus terrestris L. J Ultrastruc Res. 77:233-240.
  • Kensler RW, D Goodenough. (1980) Isolation of Mouse Myocardial Gap Junctions. J Cell Biol. 86:755-764.
  • Brink P, RW Kensler, MM Dewey. (1979) The Effect of Lanthanum on the Nexus of ABRM. Am J Anatomy 154:11-26.
  • Kensler RW, P Brink, MM Dewey. (1979) The Septum of the Lateral Axon of the Earthworm. A Thin Section and Freeze-fracture Study. J Neurocytol. 8:565-590
  • Kensler RW, P Brink, MM Dewey (1977) The Nexus of Frog Ventricle. J Cell Biol 73:768-781.
  • Kensler RW, P Brink, MM Dewey (1977) Glial Cells in the Earthworm Ventral Nerve Cord Make an A-type Nexus. Am J Anatomy 149:605-611.

Selected abstracts/presentations:

  • Shaffer, J. F., R. W. Kensler. The N-terminus of Cardiac Myosin Binding Protein-C Contains Multiple Binding Sites for F-actin. Biophysics Society meeting. 2009 Meeting. Boston, MA., Feb. 28-Mar. 4, 2009

  • Paul, D., E. P. Morris, R. Kensler, J. Squire. Three-dimensional Reconstruction of the Muscle Thick Filament: Single Particle Analysis of an Asymmetric Filament. Microscopy and Microanalysis Abstract 454, Vol. 14, Supplement 1, p. 112. 2008
  • Squire, J. M., H. A. Al-Khayat, R. W. Kensler, E. P. Morris, G. W. Offer, K. W. Ranatunga, and C. Knupp. Myosin Filament Structure and Myosin Head Movements in Active Muscle. European Microscopy Congress, September 1-5, 2008
  • Kensler RW, SP Harris. (2008) Cardiac Thick Filaments: Indirect Evidence Suggesting That the Density of cMyBP-C Contributes to the “Forbidden” Meridional Reflections in Fourier Transforms. Biophysics J.
  • Kensler RW, SP Harris. (2007) Cardiac Thick Filaments from CMyBP-C Knockout Mice: Evidence for a Change in Density at One Crossbridge Level in the Absence of cMyBP-C. XXVII Foro Annual Investigacion y Educacion. Abstract R077. San Juan, PR. March 29.
  • Kensler RW, SP Harris. (2007) The Axial perturbation in the Crossbridge Arrangement is Maintained in Thick filaments from cMyBP-C Knockout Mice. Biophys. J. Supplement 20a, Abstract 1395
  • Al-Khayat H, EP Morris, JM Squire, RW Kensler, SB Marston. (2006) Vertebrate and Invertebrate Myosin Filament Structure Using Single Particle Analysis. Presented at Imperial Muscle Institute Meeting. March 2006.
  • Kensler RW, S Harris, R Moss. (2006) The Structure of Isolated Myosin Thick Filaments from cMyBP-C Knockout Mice. Biophysics J. 90:January, 2006.
  • Kensler RW. (2005) A Study of a Change in the Myosin Heavy Chain Isotype (β-MHC to α-MHC ) on the Structure of the Rabbit Cardiac Thick Filament. Presented at the XXV Foro annual de Investigacion and Education, University of Puerto Rico, March 17, 2005. Puerto Rico Health Sciences Journal.
  • Squire JM, H Al-Khyat, EP Morris, RW Kensler. (2005) Myosin Filament Structure using Single particle Analysis. Presented at the Annual Biophysics Society Meeting in February 2005. Biophys. J. 88:632a.
  • AL-Khayat HA, EP Morris, AS Powell, RW Kensler, JM Squire. (2003) 3D Structure of Vertebrate (Fish) Muscle Myosin Filaments by Single Particle Analysis. Albach Conference.
  • Sonera Y, RW Kensler. (2002) The Effect of Tannic Acid on the Structure of Isolated Chelicerate Muscle Thick Filaments. University of Puerto Rico Research Forum.
  • AL-Khayat HA, AS Powell, RW Kensler, EP Morris, JM Squire. (2002) 3-D Structure of Fish Muscle Thick Filaments by Single Particles Analysis. Presented at London Muscle Conference, September 20, 2002.
  • Squire JM, F Eakins, RW Kensler, E Morris, HA AL-Khayat. (2002) 3D-Reconstruction of Isolated Myosin Filaments in Fish Muscle. Biophys. J. 82:5a.
  • Kensler RW. (2000) Backbone Contributions to Meridional Reflections in Isolated Cardiac Thick Filaments. Biophysical Society annual meeting in New Orleans.
  • Kensler RW, F Amaguel, A Kensler. (1999) The Problem of Specimen Flattening during Negative-Staining for Electron Microscopy. XX Research and Education Forum. Puerto Rico Health Science J. 18:172.
  • Kensler RW. (1998) The Structure of Cardiac Muscle Thick Filaments. XIX Research and Education Forum. University of Puerto Rico, Abstract A78.
  • Kensler RW. (1998) Analysis of Rabbit Cardiac Muscle Thick Filaments. Biophysics J 74:A363.
  • Kensler RW. (1997) Isolation and analysis of rabbit cardiac muscle thick filaments. XVIII Research Symposium, University of Puerto Rico. April 1997.
  • Levine R, HL Sweeney, R Kensler, Z Yang. (1995) Rabbit thick filament structure reflects the state of myosin light chain phosphorylation. Biophys. J. 68:A61.