Biological Importance of Phosphorylated Peptide and Cyclic Peptide Synthesis.

 

Phosphorylated peptide

 One of the most prominent post-translational modification (PTM) is the phosphorylation of Ser, Thr and Tyr (Table 1).  These modifications that are easily reversible allow for the in vivo production of a myriad of proteins and thus manifold biological fonctions from a singly translated polypeptide that varies in their phosphorylation patterns. 

 Phosphorylation of serine or threonine - and to a lesser extent tyrosine- residues prompts conformational changes of the protein that modify their biological activity.  For example, it has long been recognized that hormones transmit information across the external membrane of the cells by activating transmembrane signalling systems that regulate the production of a fairly small number of chemical mediators, called second messengers. These messengers trigger the activities of protein kinases and phosphatases that modify the phosphorylation states of many intracellular proteins, thus accounting for the variety of action of hormones.  Thus serine, threonine and tyrosine appear to function as molecular switches during regulation of many cellular processes.

 Phosphorylation can also be involved in diseases, for instance the tau protein, for which abnormal hyperphosphorylation has been related to amyloid fibril formation in Alzheimer’s disease.

 


Table 1.  Chemical structure of commonly phosphorylated amino acid residues

  The study of a wide variety of biological processes often requires the use of phosphorylated peptide  to mimick natural processes.  There is a dramatic difference between the syntheses of simple mono phosphorylated peptide and di- or tri- phosphorylated peptide. While simple aphosphorylated peptide are routinely synthesized using solid phase peptide synthesis (SPPS) strategies, the synthesis of multi phosphorylated peptides remains a major synthetic challenge.  Indeed, these groups are bulky, charged and unstable. While synthesis of phosphorylated peptides with multiple sites of phosphorylation in close vicinity is challenging, Genosphere Biotechnologies peptide synthesis team has been succesful in synthezing biologically active phosphorylated peptides.

 Cyclic Peptide Synthesis

 Cyclic peptide synthesis can be used to prepare peptides that mimic natural structures or to obtain more stable peptide analogues.   The resulting cyclic peptide structure shows enhanced conformational stability as compared to their natural counterparts.  Cyclic peptide synthesis has been attracting considerable interest in many years. 

 Cyclization induces limited conformational flexibility of the peptides.  In addition, cyclic peptides dramatically improve resistance to proteolytic hydrolysis and degradation.

Genosphere Bioetchnologies offers on a routine basis the two principal approaches to cyclic peptide synthesis.  Ring closing may be achieved through lactam condensation or disulfide bridge oxidation.  Basically, the lactam cycle is obtained by intramolecular amide bond (-NH-CO-) formation between an amino group (-NH2) and a carboxyl group (-COOH).

 The disulfide bridge (-S-S-) formation is achieved between two sulhydryl (-SH) groups from the side chain of cysteines incorporated at any position within the peptide by thiol oxidation. With a special cyclic peptide synthesis strategy and using appropriate protecting group chemistry to prevent unwanted cyclization, we are able to offer up to three specific disulfide bridge. 

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