View source for 1aqk


==THREE-DIMENSIONAL STRUCTURE OF A HUMAN FAB WITH HIGH AFFINITY FOR TETANUS TOXOID==
<StructureSection load='1aqk' size='340' side='right'caption='[[1aqk]], [[Resolution|resolution]] 1.84&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[1aqk]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1AQK OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=1AQK FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 1.84&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=PCA:PYROGLUTAMIC+ACID'>PCA</scene></td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=1aqk FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1aqk OCA], [https://pdbe.org/1aqk PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=1aqk RCSB], [https://www.ebi.ac.uk/pdbsum/1aqk PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=1aqk ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/IGLC2_HUMAN IGLC2_HUMAN] Constant region of immunoglobulin light chains. Immunoglobulins, also known as antibodies, are membrane-bound or secreted glycoproteins produced by B lymphocytes. In the recognition phase of humoral immunity, the membrane-bound immunoglobulins serve as receptors which, upon binding of a specific antigen, trigger the clonal expansion and differentiation of B lymphocytes into immunoglobulins-secreting plasma cells. Secreted immunoglobulins mediate the effector phase of humoral immunity, which results in the elimination of bound antigens (PubMed:20176268, PubMed:22158414). The antigen binding site is formed by the variable domain of one heavy chain, together with that of its associated light chain. Thus, each immunoglobulin has two antigen binding sites with remarkable affinity for a particular antigen. The variable domains are assembled by a process called V-(D)-J rearrangement and can then be subjected to somatic hypermutations which, after exposure to antigen and selection, allow affinity maturation for a particular antigen (PubMed:17576170, PubMed:20176268).<ref>PMID:17576170</ref> <ref>PMID:20176268</ref> <ref>PMID:22158414</ref> 
== Evolutionary Conservation ==
[[Image:Consurf_key_small.gif|200px|right]]
Check<jmol>
  <jmolCheckbox>
    <scriptWhenChecked>; select protein; define ~consurf_to_do selected; consurf_initial_scene = true; script "/wiki/ConSurf/aq/1aqk_consurf.spt"</scriptWhenChecked>
    <scriptWhenUnchecked>script /wiki/extensions/Proteopedia/spt/initialview03.spt</scriptWhenUnchecked>
    <text>to colour the structure by Evolutionary Conservation</text>
  </jmolCheckbox>
</jmol>, as determined by [http://consurfdb.tau.ac.il/ ConSurfDB]. You may read the [[Conservation%2C_Evolutionary|explanation]] of the method and the full data available from [http://bental.tau.ac.il/new_ConSurfDB/main_output.php?pdb_ID=1aqk ConSurf].
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== Publication Abstract from PubMed ==
BACKGROUND: The wide range of antibody specificity and affinity results from the differing shapes and chemical compositions of their binding sites. These shapes range from discrete grooves in antibodies elicited by linear oligomers of nucleotides and carbohydrates to shallow depressions or flat surfaces for accommodation of proteins, peptides and large organic compounds. OBJECTIVES: To determine the Fab structure of a high-affinity human antitoxin antibody. To explore structural features which enable the antibody to bind to intact tetanus toxoid, peptides derived from the sequence of the natural immunogen and antigenic mimics identified by combinatorial chemistry. To explain why this Fab shows a remarkable tendency to produce crystals consistently diffracting to d spacings of 1.7-1.8 A. To use this information to engineer a strong tendency to crystallize into the design of other Fabs. STUDY DESIGN: The protein was crystallized in hanging or sitting drops by a microseeding technique in polyethylene glycol (PEG) 8000. Crystals were subjected to X-ray analysis and the three-dimensional structure of the Fab was determined by the molecular replacement method. Interactive computer graphics were employed to fit models to electron density maps, survey the structure in multiple views and discover the crystal packing motif of the protein. RESULTS: Exceptionally large single crystals of this protein have been obtained, one measuring 5 x 3 x 2 mm (l x w x d). The latter was cut into six irregular pieces, each retaining the features of the original in diffracting to high resolution (1.8 A) with little decay in the X-ray beam. In an individual Fab, the active site is relatively flat and it seems likely that the protein antigen and derivative peptides are tightly held on the outer surface without significant penetration into the interior. There is no free space to accommodate even a dipeptide between VH and VL. One of the unique features of the B7-15A2 Fab is a large aliphatic ridge dominating the center of the active site. The CDR3 of the H chain contributes significantly to this ridge, as well as to adjoining regions projected to be important for the docking of the antigen. Both the ease of crystallization and the favorable diffraction properties are mainly attributable to the tight packing of the protein molecules in the crystal lattice. DISCUSSION: The B7-15A2 active site provides a stable and well defined platform for high affinity docking of proteins, peptides and their mimotopes. The advantages for future developments are suggested by the analysis of the crystal properties. It should be possible to incorporate the features promoting crystallization, close packing and resistance to radiation damage into engineered human antibodies without altering the desired specificities and affinities of their active sites.

Three-dimensional structure of a human Fab with high affinity for tetanus toxoid.,Faber C, Shan L, Fan Z, Guddat LW, Furebring C, Ohlin M, Borrebaeck CA, Edmundson AB Immunotechnology. 1998 Jan;3(4):253-70. PMID:9530559<ref>PMID:9530559</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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<div class="pdbe-citations 1aqk" style="background-color:#fffaf0;"></div>

==See Also==
*[[Antibody 3D structures|Antibody 3D structures]]
*[[Sandbox 20009|Sandbox 20009]]
*[[3D structures of human antibody|3D structures of human antibody]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Edmundson AB]]
[[Category: Faber C]]
[[Category: Fan Z]]