Protein Structure and Function (Campbell Biology)
The specific activities of proteins result from their intricate three-dimensional architecture, the simplest level of which is the sequence of their amino acids. What can the amino acid sequence of a polypeptide tell us about the three-dimensional structure (commonly referred to simply as the “structure”) of the protein and its function? The term polypeptide is not synonymous with the term protein. Even for a protein consisting of a single polypeptide, the relationship is somewhat analogous to that between a long strand of yarn and a sweater of particular size and shape that can be knitted from the yarn. A functional protein is not just a polypeptide chain, but one or more polypeptides precisely twisted, folded, and coiled into a molecule of unique shape, which can be shown in several different types of models. And it is the amino acid sequence of each polypeptide that determines what three-dimensional structure the protein will have under normal cellular conditions.
When a cell synthesizes a polypeptide, the chain may fold spontaneously, assuming the functional structure for that protein. This folding is driven and reinforced by the formation of various bonds between parts of the chain, which in turn depends on the sequence of amino acids. Many proteins are roughly spherical (globular proteins), while others are shaped like long fibers (fibrous proteins). Even within these broad categories, countless variations exist.
A protein’s specific structure determines how it works. In almost every case, the function of a protein depends on its ability to recognize and bind to some other molecule. In an especially striking example of the marriage of form and function, the photo above shows the exact match of shape between an antibody (a protein in the body) and the particular foreign substance on a flu virus that the antibody binds to and marks for destruction. Morphine, heroin, and other opiate drugs are able to mimic endorphins because they all have a shape similar to that of endorphins and can thus fit into and bind to endorphin receptors in the brain. This fit is very specific, something like a lock and key. The endorphin receptor, like other receptor molecules, is a protein. The function of a protein—for instance, the ability of a receptor protein to bind to a particular pain-relieving signaling molecule—is an emergent property resulting from exquisite molecular order.
Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html
Date Published: August 31, 2017 Publisher: Public Library of Science Author(s): Giuseppe Legname, Heather L. True. http://doi.org/10.1371/journal.ppat.1006458 Abstract: Partial Text The PrP can exist in 2 distinct conformations: the host-encoded, physiological cellular prion protein (PrPC) and the pathogenic isoform denoted as prion (usually referred to as PrPSc). The latter plays a key role in the … Continue reading
Date Published: April 12, 2013 Publisher: Public Library of Science Author(s): Shachi Gosavi, Yaakov Koby Levy. http://doi.org/10.1371/journal.pone.0061222 Abstract: When an amino-acid sequence cannot be optimized for both folding and function, folding can get compromised in favor of function. To understand this tradeoff better, we devise a novel method for extracting the “function-less” folding-motif of a protein … Continue reading
Date Published: September 15, 2006 Publisher: Public Library of Science Author(s): Peter Virnau, Leonid A Mirny, Mehran Kardar, Robert B Russell Abstract: Our investigation of knotted structures in the Protein Data Bank reveals the most complicated knot discovered to date. We suggest that the occurrence of this knot in a human ubiquitin hydrolase might be … Continue reading
Date Published: June 13, 2014 Publisher: Public Library of Science Author(s): unknown Abstract: None Partial Text: The authors noticed an error in the Figure 2 legend. In the text, Ca+2 should read Ca2+. The authors have provided a corrected version here. Source: http://doi.org/PBIOLOGY-D-14-01894
Date Published: March 31, 2009 Publisher: Public Library of Science Author(s): Roberto Chiesa, David A Harris Abstract: The prion protein is infamous for its role in devastating neurological diseases, but its normal, physiological function has remained mysterious. A new study uses the experimentally tractable zebrafish model to obtain fresh clues to this puzzle. Partial Text: … Continue reading