Purification and characterization of the 16-kda heat-shock-responsive protein from the thermophilic cyanobacterium Synechococcus vulcanus, which is an α-crystallin-related, small heat shock protein

Abstract

A 16-kDa protein, one of the major proteins that accumulates upon heat- shock treatment in the thermophilic cyanobacterium Synechococcus vulcanus, was purified to apparent homogeneity. The N-terminal and internal amino acid sequences of the protein exhibited a homology to the α-crystallin-related, small heat shock proteins from other organisms. The protein was designated HspA. Size-exclusion chromatography and nondenaturing gel electrophoresis demonstrated that HspA formed a large homo-oligomer consisting of 24 subunits. It prevented the aggregation of porcine malic dehydrogenase at 45 °C and 50 °C and citrate synthase at 50 °C. The activity of the malic dehydrogenase, however, was not protected under these heat-shock conditions or reactivated after a shift in temperature from 45 or 50 °C to 21 °C. HspA was able to enhance the refolding of chemically denatured rabbit muscle lactate dehydrogenase in an ATP-independent manner. A homologue to the 16- kDa protein was also found to be induced upon heat-shock treatment in the mesophilic cyanobacterium Synechocystis sp. PCC 6803.