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There are a number of methods which can be used to modify the crystallization behavior of proteins.
 
There are a number of methods which can be used to modify the crystallization behavior of proteins.
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These fall into two classes:
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1. Genetic (Mutagenesis) Approach
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2. Chemical Modification
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=== Genetic/Mutagenesis Approach===
 
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=== 1. Genetic/Mutagenesis Approach===
   
This method, also called 'surface entropy-reduction mutagenesis', involves mutation of sidechains on the surface of proteins, in order to reduce the entropic cost of forming ordered intermolecular crystal contacts and thus enhance the crystallizability of proteins.
 
This method, also called 'surface entropy-reduction mutagenesis', involves mutation of sidechains on the surface of proteins, in order to reduce the entropic cost of forming ordered intermolecular crystal contacts and thus enhance the crystallizability of proteins.
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http://nihserver.mbi.ucla.edu/SER/
 
http://nihserver.mbi.ucla.edu/SER/
      
=== Chemical Modification===
 
=== Chemical Modification===
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Several methods are available:
 
Several methods are available:
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2.1. Modification of lysine residues
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====Modification of lysine residues====
    
This method, pioneered by the Rayment laboratory, involves the methylation -- under reducing conditions -- of lysine residues. This increases the hydrophobicity of the modified lysine sidechains, reduces the overall solubility of the protein, and -- for some proteins -- promotes the formation of ordered crystal contacts.  
 
This method, pioneered by the Rayment laboratory, involves the methylation -- under reducing conditions -- of lysine residues. This increases the hydrophobicity of the modified lysine sidechains, reduces the overall solubility of the protein, and -- for some proteins -- promotes the formation of ordered crystal contacts.  
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Here is a protocol for [[Lysine Methylation]].
 
Here is a protocol for [[Lysine Methylation]].
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2.2. Modification of cysteine residues  
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====Modification of cysteine residues====
    
This method involves the carboxymethylation -- under reducing conditions -- of single cysteine residues. This effectively neutralizes the cysteine residues (some of which are chemically reactive), increases the overall solubility of the protein and can help prevent aggregation and denaturation problems.
 
This method involves the carboxymethylation -- under reducing conditions -- of single cysteine residues. This effectively neutralizes the cysteine residues (some of which are chemically reactive), increases the overall solubility of the protein and can help prevent aggregation and denaturation problems.
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