Purification and characterization of basic proteins with in vitro antifungal activity from seeds of cotton, Gossypium hirsutum

Abstract

Basic proteins from seeds of cotton ( Gossypium hirsutum) were purified by a procedure involving cation exchange chromatography on carboxymethyl cellulose (CM52) and reversed phase high performance liquid chromatography (HPLC). The basic protein fraction from these seeds contains a multiplicity of vicilin-derived 9–11 kDa proteins, a 16.3 kDa protein that has an N-terminal sequence nearly identical to that of a cotton cysteine-rich small vicilin protein and a 46.3 kDa protein having an N-terminal sequence with 61% identity and 75% similarity to the cDNA-based sequence of a γ-conglutin from Lupinus angustifolius. Edman N-terminal sequencing, electrospray ionization mass spectrometry (ESMS) and literature cDNA-based sequencing data were used to define the sequences of the vicilin-derived proteins. The inferred N- and C-terminal sequences of the 9–11 kDa proteins correspond to N-terminally truncated forms of cysteine-rich small vicilin proteins (such as the 16.3 kDa protein) suggesting that both could be processed from the vicilin ( α-globulin) preproprotein. The various cotton basic proteins were found to have selective growth inhibitory activity in vitro against the filamentous fungi Botrytis cinerea, Alternaria brassicicola, Chalara elegans and Fusarium oxysporum. These proteins differ, however, from numerous other seed antifungal proteins in being neither substrates nor inhibitors of signal transduction elements such as wheat germ Ca 2+-dependent protein kinase (CDPK), rat liver cyclic AMP-dependent protein kinase (PKA) catalytic subunit (cAK), rat brain Ca 2+- and phospholipid-dependent protein kinase (PKC) and chicken gizzard calmodulin-dependent myosin light chain kinase (MLCK).