SMALL HEAT-SHOCK-PROTEIN OF METHANOCOCCUS-JANNASCHII, A HYPERTHERMOPHILE

Small heat shock proteins (sHSPs) belong to a family of 12- to 43-kDa proteins that are ubiquitous and are conserved in amino acid sequence among all organisms. A sHSP homologue of Methanococcus jannaschii, a h yperthermophilic Archaeon, forms a homogeneous multimer comprised of 2 4 monomers with a molecular mass of 400 kDa in contrast to other sHSPs that show heterogeneous oligomeric complexes. Electron microscopy ana lysis revealed a spherically shaped oligomeric structure approximate t o 15-20 nm in diameter. The protein confers thermal protection of othe r proteins in vitro as found in other sHSPs. Escherichia coil cell ext racts containing the protein were protected from heat-denatured precip itation when heated up to 100 degrees C, whereas extracts from cells n ot expressing the protein were heat-sensitive at 60 degrees C. Similar results were obtained when purified sHSP protein was added to an E. c oil cell lysate. The protein also prevented the aggregation of two pur ified proteins: single-chain monellin (SCM) at 80 degrees C and citrat e synthase at 40 degrees C.