Symmetry 2010, 2(2), 884-906; doi:10.3390/sym2020884
Article

Symmetry versus Asymmetry in the Molecules of Life: Homomeric Protein Assemblies

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Received: 27 February 2010; in revised form: 7 April 2010 / Accepted: 12 April 2010 / Published: 19 April 2010
(This article belongs to the Special Issue Symmetry of Life and Homochirality)
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Abstract: The essay is dedicated to the relation of symmetry and asymmetry-chirality in Nature. The Introduction defines symmetry and its impact on basic definitions in science and human activities. The following section Chirality of molecules reveals breifly development of notion of chirality and its significance in living organisms and science. Homochirality is a characteristic hallmark of life and its significance is presented in the section Homochirality of Life. Proteins, important constituents of living cells performing versatile functions are chiral macromolecules composed of L-amino acids. In particular, the protein assemblies are of a great importance in functions of a cell. Therefore, they have attracted researches to examine them from different points of view. Among proteins of known three-dimensional structures about 50–80% of them exist as homomeric protein complexes. Protein monomers lack any intrinsic, underlying symmetry, i.e. enantiomorphic protein molecules involve left-handed amino acids but their asymmetry does not appear to extend to the level of quaternary structures (homomeric complexes) as observed by Chothia in 1991. In the section Homomeric assemblies we performed our analysis of very special cases of homomers revealing non-crystallographic symmetry in crystals. Homochiral proteins can crystallize only in enantiomorphic space groups. Among 230 existing space groups 65 are enantiomorphic containing limited symmetry elements that are rotation and screw-rotation axes. Any axis of rotation symmetry of a crystal lattice must be two-fold, three-fold, four-fold, or six-fold. Five-fold, seven-fold, and higher-fold rotation symmetry axes are incompatible with the symmetry under spatial displacement of the three-dimensional crystal lattice.
Keywords: homomeric proteins; symmetry; left-right asymmetry; molecular chirality; crystallographic symmetry; non-crystallographic symmetry
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Kojić-Prodić, B.; Štefanić, Z. Symmetry versus Asymmetry in the Molecules of Life: Homomeric Protein Assemblies. Symmetry 2010, 2, 884-906.

AMA Style

Kojić-Prodić B, Štefanić Z. Symmetry versus Asymmetry in the Molecules of Life: Homomeric Protein Assemblies. Symmetry. 2010; 2(2):884-906.

Chicago/Turabian Style

Kojić-Prodić, Biserka; Štefanić, Zoran. 2010. "Symmetry versus Asymmetry in the Molecules of Life: Homomeric Protein Assemblies." Symmetry 2, no. 2: 884-906.


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