STRUCTURE VS. FUNCTION IN MYOSIN LIGHT CHAIN KINASE

The long-term goal of this project is to gain a better understanding of the
physiology and biochemistry of smooth muscle contraction. Regulation of
smooth muscle contraction is by the Ca2+-calmodulin-dependent enzyme myosin
light chain kinase (MLCK) that phosphorylates the regulatory light chain of
myosin. Phosphorylation is a prerequisite for actin activation of myosin
ATPase and contraction. It has been proposed that MLCK contains an
inhibitory region that is regulated by calmodulin-binding. MLCK also
contains a catalytic region and an actin-binding region. The function of
the carboxy-terminus (approximately 24 kDa) is unknown, but preliminary
evidence suggests that this portion is expressed independent of MLCK. The
isolation of a partial cDNA for this enzyme makes it possible to use
molecular biology techniques to further knowledge in this area by defining
the relationship between the structure of these domains and function. This
cDNA is 60% complete and includes the carboxy terminus, but the sequence of
the amino terminal end of the molecule is unknown. The specific aims,
proposed are: 1) Establish a bacterial system for the expression of active
and Ca2+-calmodulin-dependent enzyme using the partial cDNA; 2) Define the
domains contained within the partial cDNA using site-directed and deletion
mutagenesis; 3) Determine the full-length sequence for MLCK by isolation of
cDNA clones that extend the 5'-end of the partial cDNA; and 4) Characterize
a new acidic protein (24 kDa) that has been isolated from smooth muscle and
is thought to be identical with the carboxy-terminus of MLCK. MLCK is a key regulatory component in smooth muscle and a clear
understanding of its mechanism is vital to our appreciation of normal
smooth muscle function. This is a prerequisite for treatment of abnormal
smooth muscle behavior; an important example is vascular smooth muscle.
These studies will help in the design of pharmacological agents for the
treatment of abnormal function.