Structure protein-like

A protein called keratin is insoluble in water but binds to other keratin molecules to form hard structures. Proteins like keratin are... 

This CDK requires the cydin-related proteins p35 or p39 as activating subunits. CDK5 (review Dhavan and Tsai, 2001) regulates the architecture of cells of the nervous system by phosphorylation of structural proteins like dynamin, tau protein, and actin. Misregulation of CDK5 by assodation with a truncated form of p35 has been implicated in the pathogenesis of Alzheimer s desease. 

A protein called keratin is insoluble in water but binds to other keratin molecules to form hard structures. Proteins like keratin are known as structural proteins or fibrous proteins. Keratin is the main component in hair and fingernails. A different protein called insulin is soluble in water and achieves a certain shape as an individual molecule. Proteins like insulin are known as globular proteins. Insulin in the bloodstream regulates glucose metabolism. 

Nature employs TM ions in many diverse ways but the most significant for the present purpose is to mediate redox chemistry. Hence, the coverage will be restricted to TM systems which are associated with a change in the metal s oxidation state. This admittedly subjective choice basically precludes zinc enzymes like, for example, carbonic anhydrase, and structural proteins like the zinc fingers but is further justified here in that the theoretical treatment of zinc systems is, compared to redox-active TM species, substantially easier. We will concentrate on metalloenzymes and, in particular, on the catalytic chemistry occurring at the active site. 

They are important components of connective tissues such as cartilage, and keratin that forms hair, nails, hooves, animal shells, etc. Other structural proteins, like myosin and kinesin, are globular proteins, which are crucial for cellular mobility of single-cellular organisms and the sperm of many multicellular organisms. 

Figure 17.16 Ribbon diagram representations of the structures of domain B1 from protein G (blue) and the dimer of Rop (red). The fold of B1 has been converted to an a-helical protein like Rop by changing 50% of its amino acids sequence. (Adapted from S. Dalai et al.,...

Starting from the protein sequence (primary structure) several algorithms can be used to analyze the primary structure and to predict secondary structural elements like beta-strands, turns, and helices. The first algorithms from Chou and Fasman occurred already in 1978. The latest algorithms find e.g., that predictions of transmembrane... 

If the sequence of a protein has more than 90% identity to a protein with known experimental 3D-stmcture, then it is an optimal case to build a homologous structural model based on that structural template. The margins of error for the model and for the experimental method are in similar ranges. The different amino acids have to be mutated virtually. The conformations of the new side chains can be derived either from residues of structurally characterized amino acids in a similar spatial environment or from side chain rotamer libraries for each amino acid type which are stored for different structural environments like beta-strands or alpha-helices. 

Sequence-specific heteropolymers, as a class of synthetic molecules, are unique in that they must be made by chemical steps that add one monomer unit at a time. Moreover, to create truly protein-like structures, which typically have chain lengths of at least 100 monomers and a diverse set of 20 side chains (or more), extremely efficient and rapid coupHngs under general reaction conditions are necessary. For these reasons, soHd-phase synthesis is typically used, so that excess reagents can be used to drive reactions to completion, and subsequent reaction work-ups are quite rapid. 

The first elastomeric protein is elastin, this structural protein is one of the main components of the extracellular matrix, which provides stmctural integrity to the tissues and organs of the body. This highly crosslinked and therefore insoluble protein is the essential element of elastic fibers, which induce elasticity to tissue of lung, skin, and arteries. In these fibers, elastin forms the internal core, which is interspersed with microfibrils [1,2]. Not only this biopolymer but also its precursor material, tropoelastin, have inspired materials scientists for many years. The most interesting characteristic of the precursor is its ability to self-assemble under physiological conditions, thereby demonstrating a lower critical solution temperature (LCST) behavior. This specific property has led to the development of a new class of synthetic polypeptides that mimic elastin in its composition and are therefore also known as elastin-like polypeptides (ELPs). 

Important products derived from amino acids include heme, purines, pyrimidines, hormones, neurotransmitters, and biologically active peptides. In addition, many proteins contain amino acids that have been modified for a specific function such as binding calcium or as intermediates that serve to stabilize proteins—generally structural proteins—by subsequent covalent cross-hnk-ing. The amino acid residues in those proteins serve as precursors for these modified residues. Small peptides or peptide-like molecules not synthesized on ribosomes fulfill specific functions in cells. Histamine plays a central role in many allergic reactions. Neurotransmitters derived from amino acids include y-aminobutyrate, 5-hydroxytryptamine (serotonin), dopamine, norepinephrine, and epinephrine. Many drugs used to treat neurologic and psychiatric conditions affect the metabolism of these neurotransmitters. 

Conversion of dipolar coupling data into three-dimensional structures presents a major challenge for folded proteins and for not-folded proteins, an additional set of obstacles must be confronted (Ackerman and Shortle, 2002). Nevertheless, the correlation of dipolar couplings measured under two sets of conditions establishes that the structures are likely to be highly similar. 

Because simple lattice models take no account of local directional preferences, they fail to model these important local restraints on protein structure. Instead, they rely almost entirely on long-range interactions to encode the most stable conformation(s) (Dill et al., 1995). Thus the ability of lattice models to reproduce protein-like behavior must be called into question. And though their simplicity makes them intellectually attractive, their use in teaching and modeling protein-like behavior must be qualified with a caveat that local directional preferences have been ignored. 

Fig. 4.19 Preparation of a protein-like structure in an inorganic mesostructured framework (Proteosilica) as a transparent film using polypeptide-functionalized surfactants.

Many extracellular proteins like immunoglobulins, protein hormones, serum albumin, pepsin, trypsin, ribonuclease, and others contain one or more indigenous disulfide bonds. For functional and structural studies of proteins, it is often necessary to cleave these disulfide bridges. Disulfide bonds in proteins are commonly reduced with small, soluble mercaptans, such as DTT, TCEP, 2-mercaptoethanol, thioglycolic acid, cysteine, etc. High concentrations of mercaptans (molar excess of 20- to 1,000-fold) are usually required to drive the reduction to completion. 

Because of the structure-function relationship for (globular) proteins, adsorption-induced changes in the molecular structure are likely to affect the biological activity of the protein, e.g., the enzymatic activity. In soils, as well as in a wide variety of other systems, the impact on biological... 

The copolymer-based systems possessing the core-shell structure in solutions are known and studied rather well (see, e.g., [14-16]). These copolymers in aqueous media tend to form polymeric micelles, which are often considered as promising drug delivery nano-vehicles [ 17,18], i.e., these macromolecular systems are not only of scientific, but also of considerable applied significance. Among such systems there are interesting examples, whose properties are very similar to the properties that should be inherent in the protein-like copolymers. All of these macromolecules possess the primary structure of... 

---