An acidified thermostabilizing mini-peptide derived from the carboxyl extension of the larger isoform of the plant Rubisco activase.

Thermostable fusion peptide partners are valuable in engineering thermostability in proteins. We evaluated the Arabidopsis counterpart (AtRAce) and an acidified derivative (mRAce) of the conserved carboxyl extension (RAce) of plant Rubisco activase (RCA) for their thermostabilizing properties in Escherichia coli and Saccharomyces cerevisiae using a protein fusion strategy. We used AtRAce and mRAce as fusion tails for the thermolabile protein RCA2 from Arabidopsis thaliana and Nicotiana tabacum. The homologous fusion of AtRAce with Arabidopsis RCA2 and the heterologous fusion of AtRAce with tobacco RCA2 increased the thermostability of both proteins. The acidified derivative mRAce conferred greater thermostability upon both proteins as compared with AtRAce. Moreover, mRAce enhanced the thermostability of other two thermolabile proteins from Jatropha curcas: the cytosolic ascorbate peroxidase 1 (JcAPX1) and the TATA-box binding protein isoform 1 (JcTBP1). We further report - for the first time - that JcTBP1 mediates heat tolerance in vivo in yeast. Thus, our study identifies a C-terminal acidic mini-peptide - the acidified derivative mRAce - with potential uses in improving the thermostability of heat-labile proteins and their associated heat tolerance in host organisms.