CHRK1, a chitinase-related receptor-like kinase in tobacco

A cDNA encoding a chitinase-related receptor like kinase, designated CHRK1, was isolated from tobacco (Nicotiana tabacum). The C-terminal kinase domai n (KD) of CHRK1 contained all of the conserved amino acids of serine/threon ine protein kinases. The putative extracellular domain was closely related to the class V chitinase of tobacco and to microbial chitinases. CHRK1 mRNA accumulation was strongly stimulated by infection with fungal pathogen and tobacco mosaic virus. Amino acid-sequence analysis revealed that the chiti nase-like domain of CHRK1 lacked the essential glutamic acid residue requir ed for chitinase activity. The recombinant chitinase-like domain did not sh ow any catalytic activity for either oligomeric or polymeric chitin substra tes. The recombinant KD of CHRK1 exhibited autophosphorylation, but the mut ant KD with a mutation in the essential ATP-binding site did not, suggestin g that CHRK1 encoded a functional kinase. CHRK1 was detected in membrane fr actions of tobacco BY2 cells. Furthermore, CHRK1-GFP fusion protein was loc alized in plasma membranes when it was expressed in animal cells. This is t he first report of a new type of receptor-like kinase containing a chitinas e-like sequence in the putative extracellular domain.