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In biology literature, the term topology is also used to refer to mutual orientation of regular secondary structures, such as alpha-helices and beta strands in protein structure [3]. For example, two adjacent interacting alpha-helices or beta-strands can go in the same or in opposite directions.
The generation of a protein sequence is much easier than the determination of a protein structure. However, the structure of a protein gives much more insight in the function of the protein than its sequence. Therefore, a number of methods for the computational prediction of protein structure from its sequence have been developed. [39]
Folded, 3-D structure of ribonuclease A. Anfinsen's dogma, also known as the thermodynamic hypothesis, is a postulate in molecular biology.It states that, at least for a small globular protein in its standard physiological environment, the native structure is determined only by the protein's amino acid sequence. [1]
A representation of the 3D structure of the protein myoglobin showing turquoise α-helices. This protein was the first to have its structure solved by X-ray crystallography. Toward the right-center among the coils, a prosthetic group called a heme group (shown in gray) with a bound oxygen molecule (red).
Predicting protein tertiary structure from only its amino sequence is a very challenging problem (see protein structure prediction), but using the simpler secondary structure definitions is more tractable. Early methods of secondary-structure prediction were restricted to predicting the three predominate states: helix, sheet, or random coil.
In proteins in general all four beta turn types occur frequently but I is most common, followed by II, I' and II' in that order. Beta turns are especially common at the loop ends of beta hairpins ; they have a different distribution of types from the others; type I' is the most common, followed by types II', I and II.
Early attempts at using in-cell NMR to study protein quinary structure were hindered by a limitation caused by the very phenomenon they were trying to understand. Many probe proteins tested in these experiments turned out to produce broad signals, near the detection limit of the method, when measured inside cells of Escherichia coli. In ...
Alpha-helical proteins are present in the inner membranes of bacterial cells or the plasma membrane of eukaryotic cells, and sometimes in the bacterial outer membrane. [5] This is the major category of transmembrane proteins. In humans, 27% of all proteins have been estimated to be alpha-helical membrane proteins. [6]