Chirality proteins

DK Lloyd, S Li, P Ryan. Protein chiral selectors in free-solution capillary electrophoresis and packed-capillary electrochromatography. J Chromatogr A 694 285-296, 1995. 

Chiral CBH (cellobiohydrolase-I protein) Chiral AGP (a j -acid glycoprotein),... 

The use of a convective macroporous polymer as an alternative support material instead of silica for the preparation of protein-based CSPs has successfully been demonstrated by Hofstetter et al. [221]. Enantioseparation was performed using a polymeric flow-through-type chromatographic support (POROS-EP, 20 pm polymer particles with epoxy functionalities) and covalently bound BSA as chiral SO. Using flow rates of up to 10 ml/min, rapid enantiomer separation of acidic compounds, including a variety of amino acid derivatives and drugs, could be achieved within a few minutes at medium efficiencies, typical for protein chiral stationary phases (Fig. 9.13). 

Mohammad J, Li YM, El-Ahmad M, Nakazato K, Pettersson G, and Hjerten S. Chiral-recognition chromatography of 3-blockers on continuous polymer beds with immobilized ceUulase as enantioselective protein. Chirality 1993 5 464 70. 

Isaksson, R., Pettersson, G. Studies on the enantioselective retention mechanisms of cellobiohydrolase I (CBH I) by covalent modification of the intact and fragmented protein, Chirality, 1998,10, 760-769. 

Calleri, E., De Lorenzi, E., Siluk, D., Markuszewski, M., Kaliszan, R., Massolini, G. Riboflavin binding protein — chiral stationary phase investigation of retention mechanism, Chromatographia,... 

Fernandez, C. Gimenez, F. Thuillier, A. Farinotti, R. Stereoselective binding of zopiclone to human plasma proteins. Chirality 1999, 11, 129-132. 

At this point, efforts were made to determine which methyl stereoisomer preferably bound to the c-Met protein. Chiral chromatographic separation of the racemic compound 5 and biological assessment of the resulting enantiomers demonstrated that... 

Magnetic circular dicliroism (MCD) is independent of, and thus complementary to, the natural CD associated with chirality of nuclear stmcture or solvation. Closely related to the Zeeman effect, MCD is most often associated with orbital and spin degeneracies in cliromophores. Chemical applications are thus typically found in systems where a chromophore of high symmetry is present metal complexes, poriihyrins and other aromatics, and haem proteins are... 

Eleven chirality centers may seem like a lot but it is nowhere close to a world record It is a modest number when compared with the more than 100 chirality centers typ ical for most small proteins and the thousands of chirality centers present m nucleic acids A molecule that contains both chirality centers and double bonds has additional opportunities for stereoisomerism For example the configuration of the chirality center m 3 penten 2 ol may be either R or S and the double bond may be either E or Z There fore 3 penten 2 ol has four stereoisomers even though it has only one chirality center... 

Glycine is the simplest ammo acid and the only one m Table 27 1 that is achiral The a carbon atom is a chirality center m all the others Configurations m ammo acids are normally specified by the d l notational system All the chiral ammo acids obtained from proteins have the l configuration at their a carbon atom meaning that the amine group IS at the left when a Fischer projection is arranged so the carboxyl group is at the top... 

Although all the chiral ammo acids obtained from proteins have the l configura tion at their a carbon that should not be taken to mean that d ammo acids are unknown In fact quite a number of d ammo acids occur naturally d Alanine for example is a constituent of bacterial cell walls and d senne occurs m brain tissue The point is that D ammo acids are not constituents of proteins... 

A novel technique for dating archaeological samples called ammo acid racemiza tion (AAR) IS based on the stereochemistry of ammo acids Over time the configuration at the a carbon atom of a protein s ammo acids is lost m a reaction that follows first order kinetics When the a carbon is the only chirality center this process corresponds to racemization For an ammo acid with two chirality centers changing the configuration of the a carbon from L to D gives a diastereomer In the case of isoleucme for example the diastereomer is an ammo acid not normally present m proteins called alloisoleucme... 

Except for glycine which is achiral all of the a ammo acids present m proteins are chiral and have the l configuration at the a carbon... 

Chiral Chromatography. Chiral chromatography is used for the analysis of enantiomers, most useful for separations of pharmaceuticals and biochemical compounds (see Biopolymers, analytical techniques). There are several types of chiral stationary phases those that use attractive interactions, metal ligands, inclusion complexes, and protein complexes. The separation of optical isomers has important ramifications, especially in biochemistry and pharmaceutical chemistry, where one form of a compound may be bioactive and the other inactive, inhibitory, or toxic. 

Biological systems depend on specific detailed recognition of molecules that distinguish between chiral forms. The translation machinery for protein synthesis has evolved to utilize only one of the chiral forms of amino acids, the L-form. All amino acids that occur in proteins therefore have the L-form. There is, however, no obvious reason why the L-form was chosen during evolution and not the D-form... 

Separation of enantiomers by physical or chemical methods requires the use of a chiral material, reagent, or catalyst. Both natural materials, such as polysaccharides and proteins, and solids that have been synthetically modified to incorporate chiral structures have been developed for use in separation of enantiomers by HPLC. The use of a chiral stationary phase makes the interactions between the two enantiomers with the adsorbent nonidentical and thus establishes a different rate of elution through the column. The interactions typically include hydrogen bonding, dipolar interactions, and n-n interactions. These attractive interactions may be disturbed by steric repulsions, and frequently the basis of enantioselectivity is a better steric fit for one of the two enantiomers. ... 

A second method uses sodium periodate (NaI04) as the oxidant in the presence of the readily available protein bovine serum albumin. In this procedure, the sulfide is complexed in the chiral envirorunent of the protein. Although the oxidant is achiral, it encounters the sulfide in a chiral envirorunent in which the two faces of the sulfide are differentiated. 

Eleven chirality centers may seem like a lot, but it is nowhere close to a world record. It is a modest number when compared with the more than 100 chirality centers typical for most small proteins and the thousands of chirality centers present in nucleic acids. 

---