Combinations of turns in proteins

Area of Science:

• Structural biology
• Protein structure analysis

Background:

• Beta- and gamma-turns are key secondary structure elements in proteins.
• Understanding turn associations can elucidate protein loop structures and functions.

Purpose of the Study:

• To investigate the association of beta- and gamma-turns into larger peptide structures.
• To identify the characteristics and prevalence of these turn-associated peptides in protein structures.

Main Methods:

• Analysis of a non-redundant dataset of 248 protein crystal structures from the Protein Data Bank.
• Identification and characterization of peptides formed by combinations of beta- and gamma-turns.
• Statistical analysis of peptide frequency, length, and associated protein types.

Main Results:

• Observed peptides ranging from 9 to 26 amino acid residues, often corresponding to protein loops.
• Nearly 40% of protein chains contained two or more such peptides; 9- and 10-residue peptides were most frequent.
• Approximately 80% of peptides included type IV beta-turns, associated with irregular dihedral angles, suggesting a role in conformational diversity.
• Predominant stabilizing interactions involved solvent, hydrogen bonds, salt bridges, and non-bonded interactions.
• Peptides were commonly found in hydrolase, oxidoreductase, transferase, and lyase protein families.

Conclusions:

• Beta- and gamma-turns associate into significant peptide structures that contribute to protein loop conformation and diversity.
• The prevalence and characteristics of these turn-associated peptides offer insights into protein structural dynamics.
• These findings are particularly relevant for understanding the function of proteins involved in catalysis and electron transfer.