We are interested in the mechanism of how muscle function
is controlled at the molecular level. Muscle contraction
is the result of repetitive cyclic interactions of two proteins,
actin and myosin. The resting state of muscle is maintained
by regulatory proteins which prevent this interaction. Calcium
triggers contraction by binding to the regulatory proteins,
and reversing their inhibitory function. Contraction may
be inhibited by regulatory components that block sites on
actin or by components that block sites on myosin. Myosin
linked regulation was discovered in our laboratory and involves
both small subunits of myosin, the regulatory and the essential
light chains. This type of regulation is widely distributed
in invertebrates, and a variant of it operates also in the
smooth muscles of vertebrates. The best system for the study
of myosin based control is the striated muscle of the scallop,
since the regulatory light chains can be removed from, and
readded to scallop myosin. In the absence of regulatory
light chains, the muscle can contract but is unable to relax.
When regulatory light chains are readded, control is fully
restored and the calcium dependency of contractile functions,
such as ATPase activity and tension development, is regained.
We are employing chemical and genetic modifications to
characterize the "on" and "off" state
of muscle and to follow the structural rearrangement the
subunits undergo when the muscle is triggered into activity.
We have isolated from myosin a small fragment that binds
both light chains and retains the triggering calcium binding
sites. This regulatory complex has been crystallized and
its structure determined in Prof. Carolyn
Cohen's laboratory. With site directed mutagenesis we
alter specific residues of the light chains and the heavy
chain of myosin to identify those amino acid residues and
peptide sequences that are responsible for various aspects
of regulatory functions such as calcium binding, interactions
of light and heavy chains of myosin, inhibition of contractile
activity and the location of the light chains on myosin.
The combined approaches of structural studies and in
vitro mutagenesis help us to clarify the molecular events
responsible for the resting and active states of muscle.
Selected Publications:
Dipesh Risal, S. Gourinath, Daniel M .Himmel, Andrew G.
Szent-Györgyi and Carolyn Cohen. (2004). Myosin subfragment
1 structures reveal a partially bound nucleotide and a complex
salt bridge that helps couple nucleotide and actin binding.
Proc. Natl. Acad. Sci. USA 101: 8930-6935.
[abstract]
Andrew G. Szent-Györgyi (2004). Milestone in Physiology:
The Early History of the Biochemistry of Muscle Contraction.
J. Gen. Physiol. 123: 631-641.
Gourinath S, Himmel DM, Brown JH, Reshetnikova L, Szent-Gyorgyi
AG, Cohen C. (2003) Crystal structure of scallop myosin
S1 in the pre-power stroke state to 2.6 a resolution: flexibility
and function in the head. Structure. 11:1621-7.
[abstract]
Nyitrai M, Stafford WF, Szent-Gyorgyi AG, Geeves MA. (2003)
Ionic interactions play a role in the regulatory mechanism
of scallop heavy meromyosin. Biophys J. 85:1053-62.
[abstract]
Nitao LK, Loo RR, O'Neall-Hennessey E, Loo JA, Szent-Gyorgyi
AG, Reisler E. (2003) Conformation and dynamics of the SH1-SH2
helix in scallop myosin. Biochemistry. 42:7663-74.
[abstract]
Nyitrai M, Szent-Gyorgyi AG, Geeves MA. (2003) Interactions
of the two heads of scallop (Argopecten irradians) heavy
meromyosin with actin: influence of calcium and nucleotides.
Biochem J. 370(Pt 3):839-48. [abstract]
Himmel DM, Gourinath S, Reshetnikova L, Shen Y, Szent-Gyorgyi
AG, Cohen C. (2002) Crystallographic findings on the internally
uncoupled and near-rigor states of myosin: further insights
into the mechanics of the motor. Proc Natl Acad Sci U
S A. 99:12645-50. [abstract]
Nyitrai M, Szent-Gyorgyi AG, Geeves MA. (2002) A kinetic
model of the co-operative binding of calcium and ADP to
scallop (Argopecten irradians) heavy meromyosin. Biochem
J. 365(Pt 1):19-30.[abstract]
Stafford WF, Jacobsen MP, Woodhead J, Craig R, O'Neall-Hennessey
E, Szent-Gyorgyi AG. (2001) Calcium-dependent structural
changes in scallop heavy meromyosin. J Mol Biol.
307:137-47. [abstract]
Houdusse A, Szent-Gyorgyi AG, Cohen C. (2000) Three conformational
states of scallop myosin S1. Proc Natl Acad Sci U S A.
97:11238-43. [abstract]
Houdusse A, Kalabokis VN, Himmel D, Szent-Gyorgyi AG, Cohen
C. (1999) Atomic structure of scallop myosin subfragment
S1 complexed with MgADP: a novel conformation of the myosin
head. Cell. 97:459-70. [abstract]
Szent-Gyorgyi AG, Kalabokis VN, Perreault-Micale CL. (1999)
Regulation by molluscan myosins. Mol Cell Biochem.
190:55-62. [abstract]
Kalabokis VN, Szent-Gyorgyi AG. (1998) Regulation of scallop
myosin by calcium. Cooperativity and the "off" state. Adv
Exp Med Biol. 453:235-40. [abstract]
Matulef K, Sirokman K, Perreault-Micale CL, Szent-Gyorgyi
AG. (1998) Amino-acid sequence of squid myosin heavy chain.
J Muscle Res Cell Motil. 19:705-12. [abstract]
Kalabokis VN, Szent-Gyorgyi AG. (1997) Cooperativity and
regulation of scallop myosin and myosin fragments. Biochemistry.
36:15834-40. [abstract]
Kalabokis, V.N., Vibert, P., York, M.L., Szent-Györgyi,
A.G. (1996). Single-headed scallop myosin and regulation.
J. Biol. Chem. 271:26779-26782. [abstract]
[full
text]
Perreault-Micale, C.L., Kalabokis, V., Nyitray, L. and
Szent-Györgyi, A.G. (1996). Sequence variations in
the surface loop near the nucleotide binding site modulate
the ATP turnover rates of molluscan myosins. J. Muscle
Res. Cell Motil. 17:543-553. [abstract]
Perreault-Micale, C.L., Jancso, A. and Szent-Györgyi,
A.G. Essential and regulatory light chains of Placopecten
striated and catch muscle myosins. (1996). J. Muscle
Res. Cell Motil. 17:533-542. [abstract]
Szent-Györgyi, A.G. (1996). Regulation of Contraction
by Calcium Binding Myosins. Biophysical Chemistry
59:357-363. [abstract]
Szent-Györgyi, A.G., Fromherz, S., Jansco, A., Nyitray,
L., and Kalabokis, V.N. (1995). Regulation of Muscle Contraction
by a Calcium-Binding Myosin: Structural and Mutational Studies.
In Calcium as Cell Signal, Proceedings of the Yamada
Conference XXXIX, pp. 65-72, Igaku-Shoin Ltd., Tokyo.
Fromherz, S and Szent-Györgyi, A.G. (1995). Role of
essential light chain EF hand domains in calcium binding
and regulation of scallop myosin. Proc. Natl. Acad. Sci.
USA 92: 7652-7656. [abstract]
Nyitray, L., Jancso, A., Ochiai, O., Graf, L. and Szent-Györgyi,
A.G. (1994). Scallop striated and smooth muscle myosin heavy-chain
isoforms are produced by alternative RNA splicing from a
single gene. Proc. Natl. Acad. Sci. USA 91:
12686-12690. [abstract]
Kalabokis, V.N., O'Neall-Hennessey, E. and Szent-Györgyi,
A.G.. (1994). Regulatory Domains of Myosins: Influence of
Heavy Chain on Calcium Binding. J. Mus. Res. Cell Motil.
15: 547-5533. [abstract]
Jancso, A. and Szent-Györgyi, A.G. (1994). Regulation
of Scallop Myosin by the Regulatory Light Chain Depends
on a Single Glycine Residue. Proc. Natl. Acad. Sci.
USA, 91: 8762-8766. [abstract]
Xie, X., Harrison, D.H., Schlichting, I., Sweet, R.M.,
Kalabokis, V.N., Szent-Györgyi, A.G. and Cohen, C.
(1994). Structure of the Regulatory Domain of Scallop Myosin
at 2.8Ä Resolution. Nature 368: 306-312.
[abstract]
[structure
info]
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