User:Mary Ball/AFP: Difference between revisions

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{{Abstract
{{Abstract
|ABSTRACT=
|ABSTRACT=
Type I antifreeze protein (AFP) from winter flounder is an alanine-rich, 37 amino acid, single alpha-helix that contains three 11 amino acid repeats (Thr-X(2)-Asx-X(7)), where X is generally Ala. <scene name='User:Mary_Ball/Sandbox/Wfb/1'>WFB</scene>
Type I antifreeze protein (AFP)are grouped according to similar structure.  The one shown is from the winter flounder.
This AFP consists of a chain of 37 amino acids that forms a single alpha-helix. Four threonines are evenly spaced in the chain, such that there are three 11-amino-acid repeats.  In the single alpha-helix that forms, the threonines all lie on one "face" of the helix.
<scene name='User:Mary_Ball/Sandbox/Wfb/1'>WFB</scene>
<scene name='User:Mary_Ball/Sandbox/Amino_acids/1'>Click here to see a labelled Ala.</scene> <scene name='User:Mary_Ball/AFP/Threonine_residues/2'>Scene with Threonine Residues Labelled</scene>  
<scene name='User:Mary_Ball/Sandbox/Amino_acids/1'>Click here to see a labelled Ala.</scene> <scene name='User:Mary_Ball/AFP/Threonine_residues/2'>Scene with Threonine Residues Labelled</scene>  
The regularly spaced Thr, Asx and Leu residues lie on one face of the helix and have traditionally been thought to form hydrogen bonds and van der Waals interactions with the ice surface. Recently, substitution experiments have called into question the importance of Leu and Asn for ice-binding. Sequence alignments of five type I AFP isoforms show that Leu and Asn are not well conserved, whereas Ala residues adjacent to the Thr, at right angles to the Leu/Asn-rich face, are completely conserved. To investigate the role of these Ala residues, a series of Ala to Leu steric mutations was made at various points around the helix. All the substituted peptides were fully alpha-helical and remained as monomers in solution. Wild-type activity was retained in A19L and A20L. A17L, where the substitution lies adjacent to the Thr-rich face, had no detectable antifreeze activity. The nearby A21L substitution had 10% wild-type activity and demonstrated weak interactions with the ice surface. We propose a new ice-binding face for type I AFP that encompasses the conserved Ala-rich surface and adjacent Thr.
 
Baardsnes, et al (1999) created mutations that reduced the protein's ice-binding ability. They also compared the sequences of five different type I AFP molecules. They found that Ala residues adjacent to the Thr were completely conserved, and concluded that the repeated Threonines, along with many of the Alanines, create one "face" of the helix adapted to bind ice crystals.
 
 
|REFERENCE=New ice-binding face for type I antifreeze protein., Baardsnes J, Kondejewski LH, Hodges RS, Chao H, Kay C, Davies PL, FEBS Lett. 1999 Dec 10;463(1-2):87-91. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/10601644 10601644]
|REFERENCE=New ice-binding face for type I antifreeze protein., Baardsnes J, Kondejewski LH, Hodges RS, Chao H, Kay C, Davies PL, FEBS Lett. 1999 Dec 10;463(1-2):87-91. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/10601644 10601644]


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(as it appears on PubMed at http://www.pubmed.gov), where 10601644 is the PubMed ID number.
(as it appears on PubMed at http://www.pubmed.gov), where 10601644 is the PubMed ID number.
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==ABOUT THIS STRUCTURE==
==ABOUT THIS STRUCTURE==
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