Biomimetics polypeptides

Abstract The aggregation behaviour of biomimetic polypeptide hybrid copolymers and copolypeptides is here reviewed with a particular eye on the occurrence of secondary structure effects. Structure elements like a-helix or / -sheet can induce a deviation from the classical phase behaviour and promote the formation of vesicles or hierarchical superstructures with ordering in the length-scale of microns. Polypeptide copolymers are therefore considered as models to study self-assembly processes in biological systems. In addition, they offer a great potential for a production of novel advanced materials and colloids. 

The phase behaviour of biomimetic polypeptide-based copolymers in solution was described and discussed with respect to the occurrence of secondary structure effects. Evidently, incorporation of crystallisable polypeptide segments inside the core of an aggregate has impact on the curvature of the corecorona interface and promotes the formation of fibrils or vesicles or other flat superstructures. Spherical micelles are usually not observed. Copolymers with soluble polypeptide segments, on the other hand, seem to behave like conventional block copolymers. A pH-induced change of the conformation of coronal polypeptide chains only affects the size of aggregates but not their shape. The lyotropic phases of polypeptide copolymers indicate the existence of hierarchical superstructures with ordering in the length-scale of microns. 

Miller s biomimetic approach inspired Ishihara [234] to develop a minimal artificial acylase for the KR of mono-protected cw-l,2-diols and A-acylated 1,2-amino alcohols. Derived from (S)-histidine, Ishihara s organocatalyst contains only one stereogenic centre and incorporates a sulfonamide linkage in place of a polypeptide chain to allow the NH group to engage as an H-bond donor with the substrates (Fig. 13) [234]. 

Employ sequential separation processes based on different physical, chemical, or biochemical properties that are synergistic, and thus orthogonal, rather than repetitive, i.e., use a metal ion-affinity HPLC procedure prior to a size-exclusion step, a hydrophobic interaction HPLC step after an ion-exchange HPLC procedure, a biomimetic HPLC step before a biospecific affinity HPLC step, etc. This rule is in accord with the orthogonality rule, which anticipates that the most efficient separation procedures are ones that take advantage of the anisotropy of molecular physicochemical properties of the target protein or polypeptide rather than the commonality of the molecular features. 

It is evident that the biomimetic approach using polypeptide hybrid polymers is very successful in the creation of novel superstructures with hierarchical order. Although started about 30 years ago in the mid-1970s, this field is still in a premature state. The greatest munber of systematic studies on the aggregation behaviour in solution is younger than 5 to 10 years. A comprehensive picture of the processes involved in the formation of hierarchical superstructures has not yet emerged. 

Fig. 3 Tripodal polypeptide used as a biomimetic supramolecular catalyst for the cleavage of phosphate esters. The tien platform is an allosteric control site. (View this art in color at www.dekker.com.)...

The acid-catalyzed polycondensation of tetraethoxysilane, a silicic acid precursor, results in the formation of an aggregated silica gel (Figure 1). Con aratively, the three-dimensional structure of die aggregated silica gel was similar to the natural morphologies of the silica particles catalyzed by proteins (9) and polypeptides (12J3J7). Furthermore, e use of external force was demonstrated (21) to control the morphology (e.g. arched, fibrillar) of a silica material catalyzed by a biomimetic silaffin peptide (i.e. a non-modified Sil Ip R5... 

There has been a report of enzyme-like activity in a block copolypeptide, which enhances the rate of hydrolysis of tetraethoxysilane (TEOS, a standard reagent in sol-gel chemistry) as a suspension in water. If this block structure is a sequence of units of a hydrophilic amino followed by units of a hydrophobic amino acid, it would be expected to be active at a water-solvent interface. The morphology of the silica that forms is dependent on the structure of the copolymer. This system is biomimetic both in the sense of employing a polypeptide catalyst and in the sense of it functioning in a multiphase system, since biological processes rarely occur in homogeneous solutions. 

Ubiqnitons channels and transporters shuttle various materials into and out of the cell as well as between different cellular compartments. Examples include porins in bacteria, nuclear pore complex in eukaryotic cells, transport of polypeptides into the endoplasmic reticulum, ion channels, and many others. Their functioning provides inspiration for the creation of biomimetic nano-transporters for technological applications. During the past decade, research of transport through biological and biomimetic transporters has seen increased application of precise and quantitative biophysical techniques that allow the resolution of the durations of the single molecule transport events on the single-channel level, in parallel with the development of the appropriate mathematical analysis tools. Combination of experimental and theoretical work has resulted in the development of a concepmal framework for the explanation of the transport specificity and efficiency of such nanochannels [42,44,45,47,48, 58-70]. 

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