Journal Article

Human Mitochondrial Hsp70 (Mortalin): Shedding Light on ATPase Activity, Interaction with Adenosine Nucleotides, Solution Structure and Domain Organization

Barbosa, Leandro R. S., Borges, Júlio C., Ramos, Carlos H. I., Dores-Silva, Paulo R.

2015

Overview

The human mitochondrial Hsp70, also called mortalin, is of considerable importance for mitochondria biogenesis and the correct functioning of the cell machinery. In the mitochondrial matrix, mortalin acts in the importing and folding process of nucleus-encoded proteins. The in vivo deregulation of mortalin expression and/or function has been correlated with age-related diseases and certain cancers due to its interaction with the p53 protein. In spite of its critical biological roles, structural and functional studies on mortalin are limited by its insoluble recombinant production. This study provides the first report of the production of folded and soluble recombinant mortalin when co-expressed with the human Hsp70-escort protein 1, but it is still likely prone to self-association. The monomeric fraction of mortalin presented a slightly elongated shape and basal ATPase activity that is higher than that of its cytoplasmic counterpart Hsp70-1A, suggesting that it was obtained in the functional state. Through small angle X-ray scattering, we assessed the low-resolution structural model of monomeric mortalin that is characterized by an elongated shape. This model adequately accommodated high resolution structures of Hsp70 domains indicating its quality. We also observed that mortalin interacts with adenosine nucleotides with high affinity. Thermally induced unfolding experiments indicated that mortalin is formed by at least two domains and that the transition is sensitive to the presence of adenosine nucleotides and that this process is dependent on the presence of Mg2+ ions. Interestingly, the thermal-induced unfolding assays of mortalin suggested the presence of an aggregation/association event, which was not observed for human Hsp70-1A, and this finding may explain its natural tendency for in vivo aggregation. Our study may contribute to the structural understanding of mortalin as well as to contribute for its recombinant production for antitumor compound screenings.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Adenosine / Adenosine - metabolism / Adenosine triphosphatase / Adenosine Triphosphatases - metabolism / Age / Agglomeration / ATPases / Biochemistry / Calorimetry / Chemistry / Circular Dichroism / Coding / Deregulation / E coli / Elongated structure / Enzyme kinetics / Escherichia coli / Heat shock proteins / HSP70 Heat-Shock Proteins - chemistry / HSP70 Heat-Shock Proteins - genetics / HSP70 Heat-Shock Proteins - metabolism / Hsp70 protein / Humans / In vivo methods and tests / Machinery / Machinery and equipment / Magnesium / Magnesium - metabolism / Mitochondria / Mitochondrial DNA / Mitochondrial Proteins - chemistry / Mitochondrial Proteins - genetics / Mitochondrial Proteins - metabolism / Models, Molecular / Nuclei / Nucleotides / p53 Protein / Protein expression / Protein Structure, Tertiary / Protein Unfolding / Proteins / Recombinant Proteins - chemistry / Recombinant Proteins - metabolism / Self-association / Small angle X ray scattering / Structure-function relationships / Tumor proteins / X ray scattering