Abstract
The prokaryotic Hsp90, HtpG, has structural properties that are similar to its eukaryotic homologue. However, its function is among the most enigmatic of the major molecular chaperones. Eukaryotes require a functional cytoplasmic Hsp90 for viability under all conditions. In contrast, HtpG is dispensable under normal growth conditions and even under heat stress in heterotrophic bacteria. Thus, function of HtpG and its cellular substrates, if any, remained to be clarified. We showed an indispensable role of HtpG for survival of the cyanobacterium Synechococcus elongatus PCC 7942 under heat and other stresses. Recently, we found that a polypeptide component of phycobilisome and uroporphyrinogen decarboxylase are in vivo protein substrates for HtpG in the cyanobacterium. We further identified the middle domain as the major chaperone site. Unlike eukaryotic Hsp90, no evidence for the interaction of HtpG with other (co)chaperones has been shown. However, we obtained evidence that HtpG collaborates with the DnaK/DnaJ/GrpE system. I will present these our recent studies which may shed light on the function of this neglected chaperone.
