Identification of in vivo substrates of the yeast mitochondrial chaperonins reveals overlapping but non-identical requirement for hsp60 and hsp10.
The mechanism of chaperonin-assisted protein folding has been mostly analyzed in vitro using non-homologous substrate proteins. In order to understand the relative importance of hsp60 and hsp10 in the living cell, homologous substrate proteins need to be identified and analyzed. We have devised a novel screen to test the folding of a large variety of homologous substrates in the mitochondrial matrix in the absence or presence of functional hsp60 or hsp10. The identified substrates have an Mr of 15-90 kDa and fall into three groups: (i) proteins that require both hsp60 and hsp10 for correct folding; (ii) proteins that completely fail to fold after inactivation of hsp60 but are unaffected by the inactivation of hsp10; and (iii) newly imported hsp60 itself, which is more severely affected by inactivation of hsp10 than by inactivation of pre-existing hsp60. The majority of the identified substrates are group I proteins. For these, the lack of hsp60 function has a more pronounced effect than inactivation of hsp10. We suggest that homologous substrate proteins have differential chaperonin requirements, indicating that hsp60 and hsp10 do not always act as a single functional unit in vivo.
Dubaquié
Y
Y
Biozentrum der Universität Basel, CH-4056 Basel, Switzerland.
Looser
R
R
Fünfschilling
U
U
Jenö
P
P
Rospert
S
S
D018835:Chaperonin 10 / Q000378:metabolism*; D018834:Chaperonin 60 / Q000378:metabolism*; D018833:Chaperonins / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D008928:Mitochondria / Q000737:chemistry*; D009154:Mutation; D014176:Protein Biosynthesis; D017510:Protein Folding; D011498:Protein Precursors / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D013379:Substrate Specificity; D013696:Temperature; D013884:Thiosulfate Sulfurtransferase / Q000737:chemistry / Q000378:metabolism
D018835:Chaperonin 10; D018834:Chaperonin 60; D011498:Protein Precursors; D012333:RNA, Messenger; D013884:Thiosulfate Sulfurtransferase; D018833:Chaperonins