Functional analysis of the Chloroplast GrpE (CGE) proteins from Arabidopsis thaliana.

The function of proteins depends on specific partners that regulate protein folding, degradation and protein-protein interactions, such partners are the chaperones and cochaperones. In chloroplasts, proteins belonging to several families of chaperones have been identified: chaperonins (Cpn60s), Hsp90s (Hsp90-5/Hsp90C), Hsp100s (Hsp93/ClpC) and Hsp70s (cpHsc70s). Several lines of evidence have demonstrated that cpHsc70 chaperones are involved in molecular processes like protein import, protein folding and oligomer formation that impact important physiological aspects in plants such as thermotolerance and thylakoid biogenesis.

A novel thioredoxin h is secreted in Nicotiana alata and reduces S-RNase in vitro.

Thioredoxins type h are classified into three subgroups. The subgroup II includes thioredoxins containing an N-terminal extension, the role of which is still unclear. Although thioredoxin secretion has been observed in animal cells, there is no evidence suggesting that any thioredoxin h is secreted in plants.