Plant Hsp100 proteins: structure, function and regulation

Hsp100/Clp family of proteins has been characterized to appreciable details in Escherichia coli, Saccharomyces cerevisiae and other such simpler biological species. In plants, yeast Hsp104-related protein was first identified in Oryza saliva. cDNA and genomic DNA clones encoding Hsp100 have been isolated and characterized from several plant species thus far. Detailed amino acid sequence analysis has revealed that Hsp100 members contain several conserved signatures. The signature sequences of various motifs of plant Hsp100 members are redefined by reducing the redundancy in this study. Based on in silico analysis, we find that a nucleotide sequence homologous to Phaseolus lunatus chloroplastic hsp100 is present in Arabidopsis genome. Yeast Hsp104 is implicated in the disaggregation of heat-inactivated proteins, thereby protecting cells during beat shock. Plant Hsp100 proteins have been shown to be functionally analogous to yeast Hsp104 by complementation studies. Hsp100 is proven to be critical for the acquisition of thermotolerance as shown by transgenic and mutation based analyses. There are indications that plant Hsp100 proteins interact and recruit components of translational machinery to specific mRNAs in order to enhance their translation. Studies on Arabidopsis thaliana, O. sativa and Zea mays reveal that besides heat stress, Hsp100 proteins are also developmentally regulated. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.