Most proteins have a primary, secondary and tertiary structure, but some of them, like hemoglobin, also have a quaternary structure. The primary structure of a protein is represented by the ordered succession of its amino acids held together by covalent bonds. While in nature amino acids may possess either the D or L configuration, amino acids within proteins almost exclusively possess the latter, as this allows proteins to have binding sites with three-dimensional properties matching those of their ligands. From an evolutionary standpoint, the existence of D-amino acids in certain proteins and peptides is highly beneficial since many D-amino acid-containing peptides participate in defense roles. This group includes antibiotic activities of secreted peptides against neighboring bacteria as well as toxic effects of psycho-active peptides on larger predators. The mode of action for these peptides involves their insertion into another organism that often possesses defense mechanisms based on stereo-specific recognition, like in the case of proteolytic enzymes and antibodies. The presence of D-amino acids prevents the host’s defense system from recognizing and degrading the peptide (Kesssel,A. and Ben-Tal N. (2011) Introduction to Proteins: Structure, Function and Motion, London: CRC Press).
Certain portions of the amino acid chain tend to fold into...
... middle of paper ...
...orrect function, as it allows molecular recognition.
(Kesssel,A. and Ben-Tal N. (2011) Introduction to Proteins: Structure, Function and Motion, London: CRC Press)
( Travaglini-Allocatelli C; Ivarsson Y, Jemth P, Gianni S (2009) Folding and stability of globular proteins and implications for function, Current Opinion in Structural Biology 19 (1): 3–7).
.( Ali, M.H and Imperiali, B. (2005) Protein oligomerization: how and why. Bioorganic and Medicinal Chemistry 13: 5013-20.)
(Ponstingl, H., Kabir, T., Gorse, D., Thornton, J.M., (2005) Morphological aspects of oligomeric protein structure, Progress in Biophysics and Molecular Biology 89: 9-35).
(Hardison, R. (1999) The Evolution of Hemoglobin: Studies of a very ancient protein suggest that changes in gene regulation are an important part of the evolutionary story, American Scientist, 87 (2): 126).
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