Comparing the modelled structures of PR-4 proteins from wheat.

Among the most frequent biochemical events following plant-pathogen interaction is the production of a heterogeneous group of pa.thogenesis-reiated (PR) proteins showing a strong antifungal activity in vitro against pathogenic fungi. These proteins were tirst described in wbacco plants infected with tobacco mosaic virus; then. a la.rge number of members of this protein family has been detected in other plant species and grouped in 1-J. classes (I). Members of some classes have a proven activity (e.g.: PR2, 13-glucanases; PR3. chitinases; PR6. proteinase mhibitors; PR9. peroxidases). some others, like PR4, have still :m unknown function. In the last yea.rs. we have isolated and sequenced four PR-4. proteins from \vheat kernels. na.med wheat win I, whea.twin2. wheatwin3 and wheatwin4 that inhibit phytopathogenic fungi with wide host range (e.g. Botrytis cinerea) :md host specific pathogens (e.g. Fusarium culmorwn. F. graminearum). Furthermore, the cDNA of wheatwinl and wheatwin2 have been cloned and the recombinant proteins expressed in £. coli . Also. the three-dimensional model of wheatwin I. based on the knowledge of the tertia.ry structure in solution of ba.rwin (4), a highly homologous protein from ba.rley, has been already designed and experimentally validated (5). Although wheatwinl and wheatwin2 differ just in two amino acid residues, their antifungal activity is different suggesting that micro-differences in the 3-D structures intluence the effectiveness of the protecting action. With the aim of obtaining information on the J.ction mechanism by the identification of structurally distinct domains that could justify the differem biological activity, we constructed the 3D models of all the proteins. In fact. if spatial atom co-ordinates of a reference protein are provided, simulation procedures can be utilised to determine the three-dimensional structure of homologous molecules. We utilised the NMR data of barwin (PDB code Ibw3) to build-up the models of all the proteins. The models were compared :md their strucrur:ll differences were discussed.