Characterization of the proteasome from the extremely halophilic archaeon Haloarcula marismortui.
A 20S proteasome, comprising two subunits alpha and beta, was purified from the extreme halophilic archaeon Haloarcula marismortui, which grows only in saturated salt conditions. The three-dimensional reconstruction of the H. marismortui proteasome (Hm proteasome), obtained from negatively stained electron micrographs, is virtually identical to the structure of a thermophilic proteasome filtered to the same resolution. The stability of the Hm proteasome was found to be less salt-dependent than that of other halophilic enzymes previously described. The proteolytic activity of the Hm proteasome was investigated using the malate dehydrogenase from H. marismortui (HmMalDH) as a model substrate. The HmMalDH denatures when the salt concentration is decreased below 2 M. Under these conditions, the proteasome efficiently cleaves HmMalDH during its denaturation process, but the fully denatured HmMalDH is poorly degraded. These in vitro experiments show that, at low salt concentrations, the 20S proteasome from halophilic archaea eliminates a misfolded protein.
Franzetti
B
B
Institut de Biologie Structurale, CNRS-CEA, 41 rue J. Horowitz, 38027 Grenoble cedex 1, France. franzetti@ibs.fr
Schoehn
G
G
Garcia
D
D
Ruigrok
R W H
RW
Zaccai
G
G
D019843:Archaeal Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D004795:Enzyme Stability; D019614:Haloarcula marismortui / Q000201:enzymology*; D007700:Kinetics; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D013816:Thermodynamics
D019843:Archaeal Proteins; D012965:Sodium Chloride; D046988:Proteasome Endopeptidase Complex