Question

1) Describe the structural features of peptide b-turns and how are they distinctly different from b-sheets.

2) Describe a spectroscopic technique for characterizing b-turn secondary structures in peptides.

Answer 1

Beta turns structural feature:

Beta turns generally called as beta bends.They are a type of secondary structure in protein.They usually link the two adjacent ends of the antiparallel segment of beta sheet.

Generally the proteins which are globular nature have the structure which is very compactly folded so they require change in direction of the peptides particularly in reverse direction.Hence, in most polypetide chains the aminoacid residuces are arranged in turns or loops.

Beta turn structure is a 180 degree turn which has four amino acid residues,in which CO(Carbonyl oxygen) of the first aminoacid residue form a hydrogen bond with the NH (amino group hydrogen) of the fourth aminoacid residue, that helps to stabilize the sudden change in direction of polypetide chains. The remaining two residues are not involved in hydrogen bonding.

In the Beta turns Glycine and Proline aminoacid residues are mostly seen.Beta turns mostly seen found near the protein surface.

Difference in Beta sheet and beta turns:

• Beta turns are non regular secondary structure whereas beta sheets are regular secondary structure
• Beta turns have four aminoacid residue which only involved in direction reversal but beta sheets are the arrangement of two peptide strands in parallel or anti parallel.
• Beta turn completely change the conformation of the polypetide chain by chain reversal ,beta sheets doesnot change confromation of polypeptide instead then run in oppossite direction.

Spectroscopic technique:

Spectroscopy is the technique which involved in the study of emission and absorption spectrum of the particular matter at particular wavelength

One of the important spectroscopic technique which is used in determination of protein's secondary structure(beta turns) is FTIR(fourier transform infrared spectroscopy).This method requires very less quantity of sample and it analyse the protein structures as quick as possible. The particular functional groups present in the beta turns like CO ,NH, H- bonding and other streching vibrations can be determined through FTIR.Which provides specific spectral peaks.Based on the spectral peak the more representative molecules of beta turns can be studied.Generally each peptide shows specific style of spectral peak that range from 500-2000 cm-1 wavenumber ,hence that will also help us to understand the how the beta turns have been formed , whether they are stable, structured properly,overlapped or not and their flexibility can also be determined.

Hope this helps you to resolve your doubts:)