Structural modeling of a plant disease resistance gene product domain

Dominant plant resistance genes are involved in the protection of plants ag ainst a wide variety of pathogens. Sequence analysis has revealed a variety of classes, often having domains in common. One commonly found region has come to be known as a putative nucleotide-binding site (NBS) due to the sim ple presence of sequence motifs. Until now, no experimental evidence has su pported this idea. Here we suggest, as an alternative hypothesis, that part of this region is structurally homologous to the receiver domain common to many proteins of His-Asp phosphotransfer pathways. This conclusion is base d on sequence analysis, threading experiments, and the construction of a mo lecular model of one domain that performs well against structure validation tools. The new hypothesis, in contrast to the NBS hypothesis, can explain the devastating effect of a Thr-->Ala mutation in a well-characterized resi stance gene product. According to the new hypothesis, regions located N-ter minal and C-terminal to the modeled portion, containing highly conserved se quence motifs, could form a separate domain. Proteins 2000;41:133-143. (C) 2000 Wiley-Liss, Inc.