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Editorial [Hot Topic: Prelude; Cellular Mechanics (Guest Editor: Yusuf Tutar)

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Machines in disrepair can either be fixed by mechanics or if they are completely damaged, they end up in a dumpster site. Proteins are machinery for function of an organism and must be strictly controlled for proper function. Heat shock proteins (Hsps) are the mechanics of almost all living organisms. By the same analogy, Hsps either help misfolded substrate proteins to reach their native conformation or send them for degradation [1]. Hsps function in a wide range of cellular processes; however their ultimate funct ion is to keep the proteins in the native conformation [1, 2]. Unfolded or partially folded proteins must reach a global free energy minimum to fold to their native state. The crowded molecular environment in a cell and hydrophobic environment of newly synthesized protein may cause protein aggregation, undesired interactions, and failure of assembling multi protein complexes [3]. Both prokaryotic and eukaryotic cells adapted a strategy to solve these problems; expressing heat shock proteins or so called “cellular mechanics”. Proposed models suggest that Hsp70s, Hsp40s and Hsp104 dissolve protein aggregates by acting together; therefore, emphasis was given on these proteins [3-5]. Hsp70 and Hsp104 were commonly studied in yeast, therefore Hsp70 and Hsp104 were further reviewed in S. cerevesiae by Dr. Jones and Dr. Chernoff, respectively. Several other Hsps are involved during substrate protein folding and prevention of aggregation. Because of their excessive number, these other proteins were not reviewed under separate topics but included under current topics. Hsp70 proteins interact with different Hsp40s to form a specialized function. Therefore, Hsp70 serves at a variety of cellular function. For this purpose, two leading groups working towards Hsp70 were invited to write reviews by emphasizing different aspects. The review by Dr. Jones specially focuses on yeast prions. The other review by Dr. Masison highlights structure-function relationship of Hsp70, Hsp70 interaction with other proteins, and Hsp70 role in signal transduction and apoptosis.

Intensive research has been done on dissolving mechanism of the aggregates by heat shock proteins and Hsp70 is at the heart of this network. Hsp100 family chops off aggregates to facilitate Hsp70-Hsp40 complex function. Hsp104 chaperone role in interactions with aggregates and with Hsp70-Hsp40 complex in yeast was reviewed by Dr. Chernoff. Unique structure of Hsp100 serves to separate chunks from aggregates. Further biological functions of Hsp104, and structure of Hsp104 were reviewed by Dr. Glover.

Hsp40 picks an unfolded protein and submits it to Hsp70. Hsp70 processes the unfolded substrate by providing a hydrophobic space. This allows a protein to fold to its native structure and makes an nonfunctional protein functional. Dr. Sha's group presented Hsp40 and its interaction with Hsp70. Classification and structure of Hsp40s were discussed in detail in order to better understand the folding of substrate peptides and solubilisation of aggregates.

Throughout this mechanism new proteins were discovered, small Hsps and nucleotide exchange factors. Dr. Kocabiyik discusses small Hsps and their essential role for inhibiting aggregate formation. In the next review, Dr. Kabani provides an overview on nucleotide exchange factors. Hsp70 encapsulates and releases substrate proteins by coupling ATP hydrolysis energy. However to start the second round, hydrolyzed ATP must be removed from Hsp70 so that another ATP can bind. Nucleotide exchange factors replace ATP for ADP in Hsp70. Detailed information on nucleotide exchange factors are given in the review.
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Document Type: Research Article

Publication date: 2009-06-01

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  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
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