Abstract
Clathrin light chains are calcium-binding proteins (Mooibroek, M. J., Michiel, D. F., and Wang, J. H. (1987) J. Biol. Chem. 262, 25-28) and clathrin assembly can be modulated by calcium in vitro. Thus, intracellular calcium may play a regulatory role in the function of clathrin-coated vesicles. The structural basis for calcium's influence on clathrin-mediated processes has been defined using recombinant deletion mutants and isolated fragments of the light chains. A single calcium-binding site, formed by residues 85-96, is present in both mammalian light chains (LCa and LCb) and in the single yeast light chain. This sequence has structural similarity to the calcium-binding EF-hand loops of calmodulin and related proteins. In mammalian light chains, the calcium-binding sequence is flanked by domains that regulate clathrin assembly and disassembly.
Highlights
Clathrin assembly can be modulated by calcium in vitro
Calcium Binding by Light Chains and Deletion Mutants-Mammalian tissues express two classes of clathrin light chain, LC. and LCb, which are the products of different genes [22, 27]
The calcium-binding site of clathrin light chains was localized to residues 71-96 by calcium-binding studies of deletion mutants and of light chain fragments
Summary
California 94143 and the llDepartment of Cell Biology, Stanford University, Stanford, California 94305. The calcium-binding sequence is flanked by domains that regulate clathrin assembly and disassembly. Mooibroek et al [6] have shown that the light chains are the calcium-binding components of the clathrin triskelion and that each light chain contributes a single calcium-binding site with a dissociation constant of 25-50 pM. A related sequence is found in the single light chain of yeast, which is shown to bind calcium. The uncoating domain’ is the target sequence for the 70-kDa heat shock cognate protein (hsc70) that depolymerizes clathrincoated vesicles (lo), whereas the region of heavy chain-light chain interaction has been shown to participate in assembly of clathrin triskelions [11]. The sequences of the calcium-binding sites of clathrin light chains appear to be modified versions of the EF hand-binding motif
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