Polyproline characterization

The next three sections (Sections 7.7.1, 7.7.2, and 7.7.3) cover fluorescence spectroscopy, I15-18 infrared, and circular dichroism, three powerful approaches to characterize the structure and conformational considerations of synthetic peptides. Section 7.7.1 deals with the use of fluorophores and broad aspects of fluorescence spectroscopy to characterize conformational aspects of peptide structure. In a similar manner, Section 7.7.2 covers a broad aspect of the uses of infrared (IR) techniques to study peptide conformations 19-22 Many IR techniques are discussed, as are approaches for the study of specific peptidic structures including amyloid, p-turn, and membrane peptides. Finally, there is a section on circular dichroism (Section 7.7.3) that covers the major issues of concern for peptide synthetic chemists such as the assignments of a-helix, 310-helix, -sheets and P-turns, and polyproline helices 23-25 There is also a brief description of cyclic peptides. 

Pioneering work by the Alix laboratory on the secondary structure of human elastin and the solubilized K-elastin, estimated the molecule to be composed of 10% a-helices, 35% P-strands and 55% undefined conformation. These estimations were based on Fourier transform infrared (FTIR), near infrared Fourier transform Raman spectroscopy and circular dichroism (CD) (15). To further investigate the nature of the elasticity, polypeptides of hydrophobic sequences containing exons 3, 7, and 30 of human elastin were analyzed by CD and Classic Raman spectroscopy, revealing polyproline II (PPII) helix secondary structures in both the aqueous and solid phase. Further analysis of exon 30 by FTIR spectroscopy determined that this sequence was characterized by both PPII as well as p-sheets structures (15). The presence of these structures were dependent on temperature, concentration and / or time, where lower temperatures and concentrations favored the PPII structure and higher temperatures and concentrations favored p-sheets (16). 

PP-fold family, a member of the gastroen-teropancreatic peptide families according to the classification proposed by Reh-feld. This family comprises pancreatic polypeptide (PP), peptide YY, and neuropeptide Y. The overall similarity in the primary structure varies between 45% and 70%. This similarity is connected to an almost identical and stable tertiary structure characterized by the PP-fold motif consisting of a polyproline-like helix (residues... 

Protein 7B2, an acidic protein (Mr 21 kDa) first isolated from porcine adenohypophysis, and characterized via cDNA sequence in humans (185 aa) and Xenopus. 7B2 is widely distributed in neural and endocrine tissues. Its sequence shows high similarities among mammals. A most conserved sequence feature is characterized by its polyproline motif (-Pro-Pro-Asn-Pro-Cys-Pro-). In neuroendocrine cells, 7B2 acts as a specific chaperone for the proprotein convertase 2 [K. L. Hsi et al., FEBS Lett. 1982, 147, 261 G. J. Martens, FEBS Lett. 1988, 234, 160 M. Mbikay et al., Biochem. 

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