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Endoplasmic reticulum quality control and apoptosis.

100%

Groenendyk J., Michalak M.

2005

vol. 52

issue 2

381-395

The ER is one of the most important folding compartments within the cell, as well as an intracellular Ca^(2+) storage organelle and it contains a number of Ca^(2+) regulated molecular chaperones responsible for the proper folding of glycosylated as well as non-glycosylated proteins. The luminal environment of the ER contains Ca^(2+) which is involved in regulating chaperones such as calnexin and calreticulin, as well as apoptotic proteins caspase-12 and Bap31, which may play an important role in determining cellular sensitivity to ER stress and apoptosis. The ER quality control system consists of several molecular chaperones, including calnexin, that assist in properly folding proteins and transporting them through the ER as well as sensing misfolded proteins, attempting to refold them and if this is not possible, targeting them for degradation. Accumulation of misfolded protein in the ER leads to activation of genes responsible for the expression of ER chaperones. The UPR mechanism involves transcriptional activation of chaperones by the membrane-localized transcription factor ATF6, in conjunction with the ER membrane kinase IRE1, as well as translational repression of protein synthesis by another ER membrane kinase PERK. When accumulation of misfolded protein becomes toxic, apoptosis is triggered, potentially with IRE1 involved in signaling via caspase-12. Both the extrinsic and intrinsic apoptotic pathways appear to culminate in the activation of caspases and this results in the recruitment of mitochondria in an essential amplifying manner. Bap31 may direct pro-apoptotic crosstalk between the ER and the mitochondria via Ca^(2+) in conjunction with caspase-12 and calnexin. Accordingly, ER stress and the resultant Ca^(2+) release must be very carefully regulated because of their effects in virtually all areas of cell function.

Structural basis of the interspecies interaction between the chaperone DnaK(Hsp70) and the co-chaperone GrpE of archaea and bacteria

75%

Żmijewski M. A., Skórko-Glonek J., Tanfani F., Banecki B., Kotlarz A., Macario A. J. L., Lipińska B.

2007

vol. 54

issue 2

245-252

Hsp70s are chaperone proteins that are conserved in evolution and present in all prokaryotic and eukaryotic organisms. In the archaea, which form a distinct kingdom, the Hsp70 chaperones have been found in some species only, including Methanosarcina mazei. Both the bacterial and archaeal Hsp70(DnaK) chaperones cooperate with a GrpE co-chaperone which stimulates the ATPase activity of the DnaK protein. It is currently believed that the archaeal Hsp70 system was obtained by the lateral transfer of chaperone genes from bacteria. Our previous finding that the DnaK and GrpE proteins of M. mazei can functionally cooperate with the Escherichia coli GrpE and DnaK supported this hypothesis. However, the cooperation was surprising, considering the very low identity of the GrpE proteins (26%) and the relatively low identity of the DnaK proteins (56%). The aim of this work was to investigate the molecular basis of the observed interspecies chaperone interaction. Infrared resolution-enhanced spectra of the M. mazei and E. coli DnaK proteins were almost identical, indicating high similarity of their secondary structures, however, some small differences in band position and in the intensity of amide I' band components were observed and discussed. Profiles of thermal denaturation of both proteins were similar, although they indicated a higher thermostability of the M. mazei DnaK compared to the E. coli DnaK. Electrophoresis under non-denaturing conditions demonstrated that purified DnaK and GrpE of E. coli and M. mazei formed mixed complexes. Protein modeling revealed high similarity of the 3-dimensional structures of the archaeal and bacterial DnaK and GrpE proteins.

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2 Acta Biochimica Polonica

1 2007

1 2005

1 Banecki B.

1 Groenendyk J.

1 Kotlarz A.

1 Lipińska B.

1 Macario A. J. L.

1 Michalak M.

1 Skórko-Glonek J.

1 Tanfani F.

1 Żmijewski M. A.

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Endoplasmic reticulum quality control and apoptosis.

Structural basis of the interspecies interaction between the chaperone DnaK(Hsp70) and the co-chaperone GrpE of archaea and bacteria