Heat Shock Proteins- Structure and Overview
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What Are Heat Shock Proteins?
Picture of HSP Chaperone
Brief Overview of the Function of Chaperones
Environmental Stress Factors
Why are Heat Shock Proteins Important?
Different Types of Heat Shock Proteins: Includes Structures
Why Don't Heat Shock Proteins Denature?
Work Cited and Bibliography
 

What are heat shock proteins?

Heat shock proteins are present in cells under normal conditions, but are expressed at high levels when exposed to a sudden temperature jump or other stress.  Heat shock proteins stabilize proteins and are involved in the folding of denatured proteins.   High temperatures and other stresses, such as altered pH and oxygen deprivation, make it more difficult for proteins to form their proper structures and cause some already structured proteins to unfold.  Left uncorrected, mis-folded proteins form aggregates that may eventually kill the cell.  Heat Shock Proteins are induced rapidly at high levels to deal with this problem.  Increased expression of HSps is mediated at multiple levels: mRNA synthesis, mRNA stability, and translation efficiency.

Most  heat shock proteins are molecular chaperones.  Chaperones aid in the transport of proteins throughout the cell's various compartments.

Under normal conditions, heat shock proteins are  required for cellular metabolism  and  help newly synthesized poly peptides fold, thus preventing  premature interactions with other proteins.
 
 

[1]  [2]  [5]  [6]

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Molecular Chaperone
The Function Of A Chaperone-Breif Overview

In a proteins unfolded state,  the hydrophobic groups will be exposed, allowing hydrophobic interactions with other poly peptide strands and thereby aggregating.  Chaperonins provide "shelters" in which new protein chains can be "incubated" until they have folded properly. [1]
[9]
Heat-denatured proteins can either aggregate to form insoluble complexes, or can be prevented from aggregating by binding to sHsps. The denatured protein can then be degraded by proteases in the cell, or refolded by ATP-dependent chaperones like HSP70.

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Environmental Stresses That Can Denature Proteins

                                                        From: Scientific American,page 41; May 1993

ENVIRONMENTAL STRESSORS
  • HEAT SHOCK
  • TRANSITION HEAVY METALS
  • INHIBITORS OF ENERGY METABOLISMS
  • AMINO ACID ANALOGUES
  • CHEMOTHERAPEUTIC AGENTS
  • STATES OF DISEASE
  • VIRAL INFECTION
  • FEVER
  • INFLAMMATION
  • ISCHEMIA
  • HYPERTROPHY
  • OXIDANT INJURY
  • MALIGNANCY
  • NORMAL CELLULAR INFLUENCES
  • CYCLE OF CELL DIVISION
  • GROWTH FACTORS
  • DEVELOPMENT AND DIFFERENTIATION
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    Why Are Heat Shock Proteins Important?

    The function of a protein is determined by its three-dimensional structure.  When excessive heat is applied to proteins, chains of amino acids which are folded into spirals, loops and sheets begin to loose their shapes.   When the interior of these proteins gets exposed, proteins can adhere and form globs.  This can make them dysfunctional.  Protein conformational defects are responsible for a number of pathologies,  ranging from Alzheimer's disease and oncogenic transformation in humans to heat and drought susceptibility in plants.  Chaperones protect against denaturization.  Heat Shock Proteins bind to denatured proteins to prevent aggregation.  Some Heat Shock Proteins, like Hsp104, have the ability to rescue already aggregated proteins.
     

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    Different Types of Heat Shock Proteins:

    Humans, fruit flies and plants all have HSPs very similar in sequence and in structure.
    Heat Shock Proteins are classified by their molecular weight, size, structure, and function.
    They are divided into several families, namely:
    HSP100
    HSP90
    HSP70
    HSP60 (chaperonin)
    and the small Heat Shock Proteins/ (alpha)-crystallin proteins

    All of the above links describe the structures of the HSPs with a brief overview of their functions.

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    Why Don't Heat Shock Proteins Denature?
    -Better Hydrogen Bonds
    -Better Hydrophobic Internal Packing
    -Enhanced Secondary Structure
    -Helix Dipole Stabilization
    [3]

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    WORK CITED AND BIBLIOGRAPHY
    [1]Adhern, Mathews, VanHold.  Biochemistry Third Edition.  NewYork: Addison Wesley Longman, Inc., 2000.

    [2]Antigenetics,LLC.  20 Oct. 2000.http://www.antigenics.com/tech/f_why.html
    Defines the importance of Heat Shock Proteins.

    [3]Jaritz, Markus.  Why Donít Heat Shock Proteins Denature?  24 June 1997.  The Mad Scientist Network.  20 Oct. 2000. http://www.madsci.org/posts/archives/aug97/867270925.Bc.r.html
    Explains why HSPs themselves are not denatured.

    [4]Landry.  GroEs Mobile Loop.  1 Dec. 1997.  Tulane University.  15 Oct. 2000. http://homeport.tcs.tulane.edu/~biochem/sam/billboard.htm
    Pictures and Structure details of GroEl and GroEs complex.

    [5]Landry.  Heat Shock and Molecular Chaperones.  1 Sept. 1998.  Tulane University.  15 Oct. 2000. http://www.tulane.edu/~biochem/med/hsp.htm
    Defines Heat Shock Proteins.  Includes functions and pictures of different types of HSPs.

    [6]Liang, P. and T.H. MacRae.  ìMolecular Chaperones And The Cytoskeletonî.  Journal of Cell Science.  Volume 110 (13) (1997): 1431-1140.  5 Oct. 2000.http://www.biologists.com/JCS/110/13/jcs8125.html
    Paper on the different kinds of HSPs, including structural and functional details.  Also discusses recent finding on heat shock proteins.

    [7]Pettitt, Jonathan.  Heat Shock Proteins.  1 Nov. 2000.  http://mcb1.ims.abdn.ac.uk/Jpet/teaching/Gde/sowhat/index.htm
    Includes a slide show of research  on heat shock proteins.

    [8]Seale, Jeff.  The Chaperonin Home Page.  17 Aug. 1998.  BiomedNet.  10 Oct. 2000. http://bioc02.uthscsa.edu/~seale/Chap/chap.html
    Discusses GroEL and GroEs  complexes in detail.  Referred to in many websites visited.

    [9]Vierling Lab.  The University Of Arizona.  1 Nov. 2000. http://www.biochem.arizona.edu/vierling/research.html
    Discusses sHSPs in detail and includes results of Vierling Lab research on sHSPs.

    All Ribbon Structures were found through the Protein Data Bank
    http://server.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Chem43.html
     

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