cDNA sequences, MALDI-TOF analyses, and molecular modelling of barley PR-5 proteins.

Barley plants are known to produce various PR-5 proteins. Transcripts encoding eight different barley PR-5 proteins (TLPs 1-8, TLP for thaumatin-like protein) were identified and cloned - seven from infected leaves and one from developing grains. Here, we describe the cDNA sequences of four of these TLP isoforms. Moreover, the TLPs from the infected leaves (TLPs 1, 2, and TLPs 4-8) were subjected to MALDI-TOF mass spectrometric measurements that resulted in protein fragments consistent with their deduced peptide sequences. Multiple sequence alignment analysis revealed that the TLPs in barley fall into two groups: long-chain proteins (TLPs 5-8) having 16 cysteine residues and short-chain proteins (TLPs 1-4) with only 10 cysteine residues. Finally, modelling experiments highlighted the effects of sequence differences between the TLP isoforms in terms of their secondary structures and their molecular electrostatic potentials. We propose that these sequence differences have implications for the target preferences of the different isomers.