A fusicoccin binding protein belongs to the family of 14-3-3 brain protein homologs.

Abstract

The fusicoccin binding protein (FCBP) is a highly conserved plasma membrane protein present in all higher plants tested thus far. It exhibits high- and low-affinity binding for the fungal toxin fusicoccin (FC). We purified the active FCBP from a fraction highly enriched in plasma membrane by selective precipitation and anion exchange chromatography. After SDS-PAGE, the two FCBP subunits of 30 and 31 kD were detected as major bands. Amino acid sequence analysis of the 31-kD polypeptide displayed a high degree of identity with so-called 14-3-3 proteins, a class of mammalian brain proteins initially described as regulators of neurotransmitter synthesis and protein kinase C inhibitors. Thereafter, we affinity purified the 30- and 31-kD FCBP subunits, using biotinylated FC in combination with a monomeric avidin column. Immunodecoration of these 30- and 31-kD FCBP subunits with polyclonal antibodies raised against a 14-3-3 homolog from yeast confirmed the identity of the FCBP as a 14-3-3 homolog. Similar to all 14-3-3 protein homologs, the FCBP seems to exist as a dimer in native form. Thus far, the FCBP is the only 14-3-3 homolog with a receptor-like function. The conserved structure of the 14-3-3 protein family is a further indication that the FCBP plays an important role in the physiology of higher plants.

Summary

“…However, addition of fusicoccin resulted in an increased amount of 14-3-3 protein associated with the membranes (Figure 9b). This is in accordance with both the observation that in vivo treatment with fusicoccin results in increased amounts of 14-3-3 protein associated with the plasma membranes of yeast cells expressing AHA2 (Figure 3) and with results of in vivo treatment of plant material with fusicoccin prior to preparation (Jahn et al, 1997;Korthout and de Boer, 1994;Oecking et al, 1994). However, pretreatment with phosphoserine-Raf-259 peptide diminished the level of 14-3-3 protein in both the control and the fusicoccin incubated plasma membranes.…”

“…In plants, pretreatment of intact tissue with fusicoccin results in an increased amount of 14-3-3 proteins associated with the plasma membrane after fractionation (Korthout and de Boer, 1994;Oecking et al, 1994Oecking et al, , 1997. The same phenomenon was observed in yeast, but only in yeast expressing full-length AHA2 (Figure 3).…”

“…Fusicoccin binding activity in plants copurifies with 14-3-3 proteins (Korthout and de Boer, 1994;Marra et al, 1994;Oecking et al, 1994). If the H ϩ -ATPase is an essential part of the fusicoccin receptor, as shown here, why do none of the aforementioned papers report the presence of the plasma membrane H ϩ -ATPase in their preparations?…”

“…14-3-3 proteins have been implicated in the co-ordination of signal transduction pathways (Aitken, 1996) and in the regulation of an increasing number of enzymes (Sehnke and Ferl, 1996). In plants, 14-3-3 proteins have been suggested to also play a role in the binding of fusicoccin (Korthout and de Boer, 1994;Marra et al, 1994;Oecking et al, 1994). Fusicoccin is known to mimic some of the physiological effects of auxin and has been used as a tool for studying the action of this phytohormone (de Boer, 1997;Marrè , 1979).…”

“…According to one model, fusicoccin interferes with a signal transduction chain ultimately leading to activation of the plant plasma membrane H ϩ -ATPase by a phosphorylation or dephosphorylation event (de Boer et al, 1994;van der Hoeven et al, 1996;Marra et al, 1994). The other model involves the fusicoccin binding protein directly regulating the H ϩ -ATPase (Marrè , 1979;De Michelis et al, 1996).…”