As biological systems have become better defined at the
molecular level, they have become increasingly amenable
to physical studies aimed at elucidating the molecular basis
of functional properties. In our research we are primarily
interested in (a) cytoskeletal filaments which control
cell shape and cell motility, and (b) membrane transport
proteins which store energy and maintain the distinctive
compositions of intracellular compartments.
(a) Cytoskeletal proteins have been the subject of intense
experimental scrutiny, but relatively little theoretical
attention. Of particular interest is the molecular basis
for the spatial organization of cytoskeletal fibers in cells.
Typically it is assumed that protein polymers should be
randomly disposed in solution and that the non-random organization
of cytoskeletal fibers must be due to the effects of various
accessory binding proteins. However, the cytosol is a very
crowded and therefore highly non-ideal solution. Under these
circumstances, the theory of liquid crystals tells us that
elongated particles may spontaneously align, coalesce into
bundles, and form gels. We are adapting these theories to
heterogeneous systems with self-assembling fibers to characterize
the various mechanisms by which cells can control the spatial
arrangement of cytoskeletal elements. We find that, under
physiological conditions, long filaments are not only predicted
to form bundles, but these bundles will be segregated according
to the diameters and flexibilities of the filaments. The
function of cross-linking by bundling proteins therefore
appears to be only to fine tune the bundles (e.g., as to
polarity and registration). The theory also predicts that
the cell can prevent crowding-induced bundling by using
its capping proteins to reduce the lengths of the filaments.
And it can frustrate bundling and form a gel by using other
accessory proteins that cross-link filaments in orthogonal
configurations.
(b) Halophilic archae produce retinal containing membrane
proteins similar to the mammalian visual pigments. These
rhodopsins include energy transducers that use light to
drive ion transport, as well as signal transducers that
use light to stimulate phototaxis. The rhodopsins are thus
light-driven analogues of the chemically-driven energy transducers
(membrane ATPases) and signal transducers (hormone receptors)
found in mammalian cells. The first rhodopsin to be discovered
in a unicellular organism (known therefore as bacteriorhodopsin)
is also the most abundant. It undergoes a photocycle in
which a proton is released on the extracellular side of
the membrane and replaced from the intracellular side of
the membrane. Thus, light is used to create a proton electrochemical
potential gradient across the membrane that the cell can
use to drive other processes. To study bacteriorhodopsin
in the native membrane, we employ solid-state NMR methods
that achieve the high resolution of solution spectra while
preserving the three-dimensional information of powder spectra.
The results are interpreted empirically using data from
model compounds and theoretically via quantum mechanical
calculations. Specifically, we are probing the conformation
of the molecule and the movement of protons along conducting
pathways, in the resting state and in photocycle intermediates,
in order to understand how the protein enforces unidirectional
transport. We focus particularly on the changes that occur
between deprotonation and reprotonation of the chromophore,
since these are the changes that are thought to prevent
backflow.
Selected Publications:
Herzfeld J. (2004) Crowding-induced organization in cells:
spontaneous alignment and sorting of filaments with physiological
control points. J Mol Recognit. 17:376-81.
[abstract]
Belenky M, Meyers R, Herzfeld J. (2004) Subunit structure
of gas vesicles: a MALDI-TOF mass spectrometry study. Biophys
J. 86(1 Pt 1):499-505. [abstract]
Petkova AT, Baldus M, Belenky M, Hong M, Griffin RG, Herzfeld
J. (2003) Backbone and side chain assignment strategies
for multiply labeled membrane peptides and proteins in the
solid state. J Magn Reson. 160:1-12. [abstract]
Herzfeld J and Lansing JC. (2002) Magnetic Resonance Studies
of the Bacteriorhodopsin Pump Cycle. Annual Reviews of
Biophysics and Biomolecular Structure 31, 73-95. [abstract]
Kandori H, Belenky M and Herzfeld J. (2002) Vibrational
frequency and dipolar orientation of the protonated Schiff
base in bacteriorhodopsin before and after photoisomerization.
Biochemistry 41, 6026-6031.
Maeda A, Balashov SP, Lugtenburg J, Verhoeven MA, Herzfeld
J, Belenky M, Gennis RB, Tomson FL and Ebrey TG. (2002)
Interaction of Internal Water Molecules with the Schiff
Base in the L Intermediate of the Bacteriorhodopsin Photocycle.
Biochemistry 41, 3803-3809.
Petkova, AT, Hatanaka M, Jaroniec CP, Hu JG, Belenky M,
Verhoeven M, Lugtenburg J, Griffin RG and Herzfeld J. (2002)
Tryptophan Interactions in Bacteriorhodopsin: A Heteronuclear
NMR Study. Biochemistry 41, 2429-2437. [abstract]
Hatcher ME, Hu JG, Belenky M, Verdegem P, Lugtenburg J,
Griffin RG and Herzfeld J. (2002) Control of the Pump Cycle
in Bacteriorhodopsin: Mechanisms Elucidated by Solid-State
NMR of the D85N Mutant. Biophysical J 82, 1017-1029.
[abstract]
Lansing JC, Hohwy M, Jaroniec CP, Creemers AFL, Lugtenburg
J, Herzfeld J and Griffin RG. (2002) Chromophore Distortions
in the Bacteriorhodopsin Photocycle: Evolution of the H-C14-C15-H
Dihedral Angle Detected by Solid-State NMR. Biochemistry
41, 431-438. [Abstract]
[Full
Article - PDF]
Jaroniec CP, Lansing JC, Tounge BA, Belenky M, Herzfeld
J and Griffin RG. (2001) Measurement of Dipolar Couplings
in a Uniformly 13C,15N-Labeled Membrane Protein: Distances
between the Schiff Base and Aspartic Acids in the Active
Site of Bacteriorhodopsin, J Am Chem Soc 123, 12929-12930.
[Full
Article - PDF]
Jaroniec CP, Tounge BA, Herzfeld J and Griffin RG. (2001)
Frequency Selective Dipolar Recoupling in Rotating Solids:
Accurate 13C‹15N Distance Measurements in Uniformly-13C,15N-labeled
Peptides. J Am Chem Soc 123, 3507-3519. [Abstract]
[Full
Article - PDF]
Kandori H, Yamazaki Y, Shichida Y, Raap J, Lugtenburg J,
Belenky M and Herzfeld J. (2001) Tight Asp85-Thr89 Association
during the Pump Switch of Bacteriorhodopsin. Proc Natl
Acad Sci USA 98, 1571-1576. [Abstract]
Rosay M, Zeri AC, Astrof NS, Opella SJ, Herzfeld J and
Griffin RG. (2001) Sensitivity-Enhanced NMR of Biological
Solids: Dynamic Nuclear Polarization of Y21M fd Bacteriophage
and Purple Membrane. J Am Chem Soc 123, 1010-1011.
[Full
Article - PDF]
Herzfeld J and Olbris DJ. Hydrophobic Effect. Encyclopedia
of Life Sciences, http://www.els.net, Nature Publishing
Group (London, 2000).
Herzfeld J, Olbris DJ, Furman E and Benderskiy V. (2000)
Structural Decomposition of the Chemical Shielding Tensor:
Contributions to the Asymmetry, Anisotropy and Orientation.
J Chem Phys 113, 5162-5170.
Jaroniec CP, Tounge BA, Rienstra CM, Herzfeld J and Griffin
RG. (2000) Recoupling of Heteronuclear Dipolar Interactions
with Rotational-echo Double-resonance at High Magic Angle
Spinning Frequencies. J Magn Reson 146, 132-139.
[Abstract]
Lanyi JK, Bizounok M, Herzfeld J, Raap J and Lugetnburg
J. (2000) Local and Distant Protein Structural Changes on
Photoisomerization of the Retinal in Bacteriorhodopsin.
Proc Natl Acad Sci USA 97, 4643-4648. [Abstract]
"NMR Probes of Vectoriality in the Proton-Motive Photocycle
of Bacteriorhodopsin: Evidence for an 'Electrostatic Steering'
Mechanism," BBA Bioenergetics, (2000), 1460, 95-105;
with Brett A. Tounge. [abstract]
"Avoidance model for soft particles. II: Positional ordering
of charged rods," Phys. Rev. E, (2000), 61, 6872-6878;
with Eric M. Kramer. [abstract]
"Early and Late M Intermediates in the Bacteriorhodopsin
Photocycle: A Solid-State NMR Study," Biochemistry,
(1998), 37, 8088-8096; with Jingui G. Hu, Boqin Q. Sun,
Marina Bizounok, Mary E. Hatcher, Jonathan C. Lansing, Jan
Raap, Peter J. E. Verdegem, Johan Lugtenburg and Robert
G. Griffin. [abstract]
"The Predischarge Chromophore in Bacteriorhodopsin: A 15N
Solid-State NMR Study of the L Photointermediate," Biochemistry
(1997), 36, 9316-9322; with Jingui G. Hu, Boqin Q. Sun,
Aneta Petkova and Robert G. Griffin. [abstract]
"Entropically-Driven Order in Crowded Solutions: from Liquid
Crystals to Cell Biology," Accounts of Chemical Research
1996, 29, 31-37.
"Crowding-induced Organization of Cytoskeletal Elements.
III. Spontaneous Bundling and Sorting of Self-assembled
Filaments with Different Flexibilities," Biophysical
Chem (1995), 57, 93-102; with D.T. Kulp. [abstract]
View Complete Publication List on PubMed:
Judith Herzfeld
Last reviewed: January 3, 2007. E-mail
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