Cellular Biochemistry Section
Edward D Korn, PhD, Principal Investigator
Members of the very large myosin superfamily have
essential roles in multiple, critical cellular processes of all
eukaryotic cells including, but not limited to, muscle contraction,
cell motility, cytokinesis, phagocytosis, organization of the cytoskeleton
and movement of intracellular organelles. Class-I myosins contain
a single heavy chain and one or more light chains while all other
myosins contain two identical heavy chains and at least four light
chains. Myosins are actin-based motors with actin-activated ATPase
activity that is coupled to mechanical and structural events involving
the actin filaments. The actin-dependent ATPase activity of different
myosins in nonmuscle cells is regulated by phosphorylation of either
the heavy chain, the light chain, or both. We are particularly interested
in the mechanisms by which light and heavy chain phosphorylation
regulate the activity of Class-I and Class-II myosins and the independent
and interdependent properties of the head and tail domains. By extensive
use of mutated myosins and chimeras of head and tail regions of
different Class-I and Class-II myosins, we are correlating the biochemical
and biophysical properties of the pure proteins in vitro to their
abilities to support specific cellular activities. Examples of recent
and current studies include the ability of chimeras comprising the
head domain of Dictyostelium myosin II and the tail domains of either
smooth muscle or Acanthamoeba myosin II to support the functions
of myosin II in Dictyostelium and the effect of substitutions in
the cardiomyopathy loop on the biochemical and biological properties
of Dictyostelium myosin II. We are also interested in the molecular
basis of the regulation of the actin-activated ATPase activity of
the head domain of Acanthamoeba myosin II by phosphorylation of
regulatory serines at the tip of the tail domain and the structure
of the tail domains of class-I myosins. Recently, our interest in
actin dynamics has been re-kindled.
Questions, comments and suggestions about this page may be addressed
to Edward
Korn
Richard W Hendler, PhD, Scientist Emeritus
The interests of this section are focused on membrane-associated
enzymes and the role of the membrane in the activity of the enzyme.
Primary attention has been on integral membrane, energy-transducing,
proton pumps, namely cytochrome oxidase and bacteriorhodopsin (BR).
The experimental approach relies heavily on computer-controlled
procedures developed in our laboratory to perform rapid kinetic
optical measurements which define steps in the enzyme-turnover and
electrical measurements to quantify energy-transducing events. With
cytochrome oxidase, we find that the electrons follow a branched
rather than a linear path from its redox centers to O2.
With BR, we have demonstrated a crucial role for specific lipids
of the membrane in the proton-pumping photocycle and its regulation
by actinic light. Work with site-directed mutants is in progress
to define the locus of the lipid-protein interaction. Our studies
with BR cover purified BR preparations, BR-proteoliposomes, isolated
cell membrane fragments containing BR, and the intact cell. In collaborations
with other laboratories, we are trying to correlate structural conformational
states of the protein with proton-pumping events using both FTIR
and NMR.
Questions, comments and suggestions about this page may be addressed
to Richard
Hendler
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