A Major Antimicrobial Hybrid Chitin-Binding Protein from French Bean with Features Common to Arabinogalactan-Proteins and Hydroxyproline-Rich Glycoproteins

A two component chitin‐binding protein from French bean – association of a proline‐rich protein with a cysteine‐rich polypeptide

“…Although a number of cDNA clones have been obtained from French bean [16,17], which contain the repeat sequence of the cognate 25 kDa PRP when translated, they differ at the C‐terminus (data not shown). A number of others isolated in the further study reported here, while having high sequence similarity to PRPs, lack the N ‐terminus sequence NYDKPPVEK of 25 KDa component, and may contain cloning artefacts due to the repetitive nature of the DNA sequences (data not shown).…”

“…The protein was characterised by an N-terminal domain typical of proline-rich proteins (PRPs) from legumes and amino acid analysis showed the presence of a high level of cysteine, which is characteristic of chitinbinding proteins [11]. The isolated protein was shown to bind to chitin with an average K L of 4.0 nM which was similar to the binding constant K L 4.2 nM of suspension cultured cells [16,17]. However, further analysis and molecular cloning was difficult because it was completely intractable to protease digestion [16] and therefore no internal sequence could be obtained to allow study of the domain structure in its entirety, although it was assumed to be a hybrid protein similar to other chitin-binding hydroxyproline rich glycoproteins from solanaceous species such as potato lectins with a cysteine-rich domain and a highly glycosylated hydroxyproline rich domain [2,18,19].…”

“…However, further analysis and molecular cloning was difficult because it was completely intractable to protease digestion [16] and therefore no internal sequence could be obtained to allow study of the domain structure in its entirety, although it was assumed to be a hybrid protein similar to other chitin‐binding hydroxyproline rich glycoproteins from solanaceous species such as potato lectins with a cysteine‐rich domain and a highly glycosylated hydroxyproline rich domain [2,18,19]. Attempts to isolate a cDNA corresponding to the N ‐terminus gave numerous related clones with the correct repeat sequence of variable length but with no in‐frame cysteine‐rich domain and this was attributed to cloning artefacts common to such highly repetitive DNA sequences and G‐C rich domains [16,17]. We now reveal that the French bean chitin‐binding protein (FBCBP) is not a hybrid but a tightly bound two‐component system that requires disruptive conditions to separate them.…”