Secondary structure - specific examples

See also Secondary Structure (General), Secondary Structure (Terms), Secondary Structures (Specific examples). Factors Determining Secondary and Tertiary Structure, Sheet, Keratin,... 

Fibrillar proteins have a specific secondary structure. For example, the basic secondary structure of keratin consists of two pairs of closely linked right-handed a-hehces (a superhehx) that are coiled into a left-handed hehx. The basic secondary structure of collagen is a triple hehx in which the left-handed polypeptide helix is coiled into the right-handed superhehx. 

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

Enrichment of the 15N content has become part of various powerful research techniques. For example, uniform labeling with 1SN was used for sequence-specific assignments and secondary structure determination of certain proteins by NMR60 and tracing of complicated processes including the increase of DON in soil61,62. 

Noncovalent interactions play a key role in biodisciplines. A celebrated example is the secondary structure of proteins. The 20 natural amino acids are each characterized by different structures with more or less acidic or basic, hydrophilic or hydrophobic functionalities and thus capable of different intermolecular interactions. Due to the formation of hydrogen bonds between nearby C=0 and N-H groups, protein polypeptide backbones can be twisted into a-helixes, even in the gas phase in the absence of any solvent." A protein function is determined more directly by its three-dimensional structure and dynamics than by its sequence of amino acids. Three-dimensional structures are strongly influenced by weak non-covalent interactions between side functionalities, but the central importance of these weak interactions is by no means limited to structural effects. Life relies on biological specificity, which arises from the fact that individual biomolecules communicate through non-covalent interactions." " Molecular and chiral recognition rely on... 

For example, in the specificity subsite S3 the phenyl rings of Phe P3 occupy almost identical positions in both renin inhibitor complexes. Modeling studies have predicted the specificity subsite S3 to be larger in renins than in other aspartic proteinases [4] due to substitution of smaller residues, Pro 111, Leul 14, and Alai 15, in place of larger ones in mammalian and fungal proteinases. However, a compensatory movement of a helix (hN2) makes the pocket quite compact and complementary to the aromatic ring as shown in Figure 5. Thus, the positions of an element of secondary structure differ between renin and other aspartic proteinases with a consequent important difference in the specificity pocket. 

Collagen and elastin are examples of common, well-characterized fibrous proteins that serve structural functions in the body. For example, collagen and elastin are found as components of skin, connective tissue, blood vessel walls, and sclera and cornea of the eye. Each fibrous protein exhibits special mechanical properties, resulting from its unique structure, which are obtained by combining specific amino acids into reg ular, secondary structural elements. This is in contrast to globular proteins, whose shapes are the result of complex interactions between secondary, tertiary, and, sometimes, quaternary structural elements. 

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