Multiplicity of clathrin light-chain-like polypeptides from developing pea (Pisum sativum L.) cotyledons

Abstract

A comparative study has been made of clathrin-coated vesicles from developing pea (Pisum sativum L.) cotyledons and bovine brains in order to characterize the clathrin light chains from a plant system. Four polypeptides of 31 kDa, 40 kDa, 46 kDa and 50 kDa are considered as candidates for clathrin light chains in the developing pea cotyledons. The 31 kDa, 40 kDa, 46 kDa and 50 kDa polypeptides, together with the 190 kDa heavy chain, are dissociated as triskelions when coated vesicles of developing pea cotyledons are treated with 2 M urea. Partially purified 46 kDa and 50 kDa polypeptides have been demonstrated to bind to purified clathrin heavy chains. The 40 kDa, 46 kDa and 50 kDa polypeptides are sensitive to elastase. They are readily solubilized by neutralization of 10% trichloroacetic acid precipitates of clathrin. The 50 kDa polypeptide of plant clathrin-coated vesicles is heat-stable as are the light chains from bovine brains, while the heat stability of the 31 kDa, 40 kDa and 46 kDa polypeptides of plants is dependent on pH and ionic strength. The 40 kDa, 46 kDa and 50 kDa polypeptides bind calmodulin. The calcium binding properties of these polypeptides are ambiguous. The 40 kDa and 46 kDa polypeptides can be phosphorylated more extensively than the 31 kDa in vitro in the presence of polylysine, as can the smaller light chain of brains. The 50 kDa polypeptide can also be phosphorylated, even without the addition of polylysine. Unlike brain light chains, phosphorylation of the 31 kDa, 40 kDa, 46 kDa and 50 kDa polypeptides from peas is greatly reduced by N-ethylmaleimide (NEM). Our findings contrast with earlier reports of clathrin light chains of 30 and 38 kDa from zucchini and 57 and 60 kDa from carrots, respectively.