Clathrin light chains and secretory vesicle binding proteins are distinct

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Cytosolic proteins binding to secretory vesicle membranes regulate exocytosis.
• Previous studies suggested chromaffin granule binding proteins are identical to clathrin light chains.
• A hypothesis proposed Ca2+-dependent light chain recruitment initiates endocytosis.

Purpose of the Study:

• To investigate the relationship between chromaffin granule membrane binding proteins and clathrin light chains.
• To determine if calmodulin is required for cytosolic protein interaction with the vesicle membrane.

Main Methods:

• Two-dimensional peptide mapping of clathrin light chains and granule binding proteins.
• Assessing the effect of calmodulin antagonism on protein-membrane association.

Main Results:

• Two-dimensional peptide maps revealed distinct structures for clathrin light chains and granule binding proteins.
• Antagonizing calmodulin with trifluoperazine did not inhibit cytosolic protein binding to the membrane.

Conclusions:

• The hypothesis linking Ca2+-dependent light chain recruitment to clathrin coat assembly is not supported.
• Calmodulin is not essential for the association of these cytosolic proteins with the chromaffin granule membrane.